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The assessment of unwanted intrusive thoughts: A review and critique of the literature
Pergamon
0005-7967(95)00030-5
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Behav. Res. Ther. Vol. 33, No. 8, pp. 967-976, 1995 Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0005-7967/95 $9.50 + 0.00
ESSAY
ASSESSMENT OF UNWANTED INTRUSIVE THOUGHTS: A REVIEW AND CRITIQUE OF THE LITERATURE DAVID A. CLARK and CHRISTINE L. PURDON Department of Psychology, University of New Brunswick, Bag Service No. 45444, Fredericton, New Brunswick, Canada E3B 6E4 (Received 10 January 1995)
Summary--In this paper we review the assessment and measurement of normal unwanted intrusive thoughts, images, and impulses that are considered the basis of clinical obsessions. After highlighting some difficulties with how the definition of cognitive intrusion has been applied to the development of assessment measures, we evaluate the construct validity of a number of retrospective self-report instruments such as the Intrusive Thoughts Questionnaire, Cognitive Intrusions Questionnaire, and Obsessional Intrusions Inventory, as well as interview and diary procedures. Measures of personal responsibility and meta-cognitive beliefs, which are still in the developmental phase, are also discussed. We conclude with a number of recommendations and areas of further research which would strengthen the construct validity of measures of intrusive thoughts and related constructs.
INTRODUCTION The sudden intrusion of unwanted or unwillful thoughts, images, or impulses is a frequent and natural occurrence within our stream of consciousness. In fact at times we seem almost helpless in our efforts to consciously control the content or direction of our thoughts (Wegner, 1992), as evidenced by the unwanted intrusion of a variety of mental events from a mundane tune or rhyme to a negative, possibly even digusting or abhorrent, thought or image. This intrusive quality of cognition may be a particularly adaptive aspect of human nature when it involves the spontaneous occurrence of positive cognitions associated with creativity, inspiration, problem solving, and relief from boredom leading to increased motivation for productive work and social interaction. (Salkovskis, 1989). In the last two decades, clinical psychologists have begun to empirically investigate the role of unwanted, distressing intrusive thoughts, images and impulses in the pathogenesis of a variety of psychopathological states, such as obsessive compulsive disorders (Rachman & Hodgson, 1980), depression (Wenzlaff, Wegner & Roper, 1988), post traumatic stress disorder (Foa, Steketee & Rothbaum, 1989), and generalized anxiety disorder (Barlow, 1988). More recently Wegner and others have investigated the intentional suppression of unwanted thoughts and the role such mental control efforts may play in the regulation of mood, behavior, and social interaction as well as psychopathology (Wegner, 1992; Wegner & Erber, 1993). The study of unwanted intrusive distressing thoughts is particularly important to current psychological theories of obsessive compulsive disorder (OCD). In a seminal monograph on the topic, Rachman (1981) defined unwanted intrusive thoughts as repetitive, unacceptable or unwanted thoughts, images or impulses that: (a) interrupt ongoing activity; (b) are attributed to an internal origin; (c) are difficult to control. Based on this definition, then, any mental phenomena that repeatedly intrudes into our mind against our will could be considered an unwanted intrusive thought. However, it is the negative, distressing cognitive intrusions that have been the primary focus of clinical researchers interested in the etiology and maintenance of obsessions. Rachman and de Silva (1978) first demonstrated that nonclinical Ss experience unwanted thoughts that are similar in form BRr 33/S~:~
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and content to clinical obsessions. Since then, a number of other studies have replicated this finding, showing that 80-99% of nonclinical Ss report unwanted and unacceptable intrusive thoughts, images, or impulses (Clark & de Silva, 1985; Edwards & Dickerson, 1987a; England & Dickerson, 1988; Freeston, Ladouceur, Thibodeau & Gagnon, 1991; Niler & Beck, 1989; Parkinson & Rachman, 1981a; Purdon & Clark, 1993; Salkovskis & Harrison, 1984). As a result, recent cognitive-behavioural theories of OCD suggest that clinical obsessions may have their origins in the unwanted ego-dystonic intrusive thoughts found in normals (Rachman, 1971, 1976; Rachman & Hodgson, 1980; Salkovskis, 1985, 1989). Because of pre-existing dysfunctional beliefs about the need to control unacceptable thoughts, and the tendency to misinterpret unwanted intrusive thoughts as an indication that they may be responsible for harm to themselves or others, the intrusions of obsession-prone individuals can escalate in frequency and severity to become clinical obsessions (Clark & Purdon, 1993; Rachman, 1993; Salkovskis, 1994). In this article we will examine the assessment of unwanted intrusive thoughts as it pertains to research on clinical obsessions. We discuss issues involving the definition of intrusive cognitions, the reliability and validity of various intrusive thoughts instruments, and recent developments in the measurement of personal responsibility and meta-cognitive beliefs, processes considered crucial in the pathogenesis of clinical obsessions. The focus of the paper is on assessment via retrospective self-report methodology rather than on the production of intrusive thoughts in experimental settings. Although the latter represents a promising area of research for understanding the uncontrollability of cognition, most of the research on obsessive intrusive thoughts has relied on self-report questionnaires or interview. D E F I N I T I O N OF U N W A N T E D INTRUSIONS The empirical investigation of cognitive constructs has proven to be particularly challenging for clinical researchers. The internal, private nature of cognition makes any evaluation of the validity of Ss' self-reports of their thoughts most difficult (Clark, 1988). One approach used by clinical researchers to increase the accuracy of their cognitive assessments is to focus on specific thought content. Examples include the Cognitions Checklist (Beck, Brown, Steer, Eidelson & Riskind, 1987) and Automatic Thoughts Questionnaire (Hollon & Kendall, 1980). These measures assess negative automatic thoughts of loss and failure or harm and danger associated with depression or anxiety, and thereby assess specific thoughts defined strictly in terms of their content domain (Beck, 1987; Beck & Clark, 1988). This same content orientation to measurement is evident in most self-report measures of worry (Davey, 1993; Tallis, Davey & Bond, 1994; Tallis, Eysenck & Matthews, 1992; Wells, 1994). We find a very different emphasis when we consider unwanted intrusive thoughts. Here the focus is not on specific thought content but rather on process characteristics. That is, any thought, image or impulse may be an unwanted intrusive thought as long as it satisfies the criteria of intrusiveness (Rachman, 1981; Grey, 1982). This process-oriented approach to defining unwanted intrusive thoughts assumes Ss can reliably and accurately discern intrusive from nonintrusive cognitions, once they are provided with a definition or description of the constructs. However, there is some evidence that Ss require examples of unwanted intrusive thoughts before they can distinguish their own cognitive intrusions (Edwards & Dickerson, 1987a; Parkinson, personal communication, 1983). This suggests that individuals may need to be provided with thought content as well as process characteristics (i.e. degree of intrusiveness, uncontrollability) before they can distinguish these cognitive phenomena in their own stream of consciousness. The importance of considering both thought content and process is evident when we attempt to distinguish between different types of cognitive phenomena such as negative automatic thoughts and unwanted intrusive thoughts. Salkovskis (1985) argues that the negative automatic thoughts (NATs) that Beck (1976, 1987) and others consider important in anxiety and depression are different from unwanted intrusive thoughts. NATs tend to be ego-syntonic, less intrusive, plausible, rational and more difficult to access, whereas obsessional intrusive thoughts tend to be ego-dystonic, highly intrusive and accessible, irrational and less plausible. As a result, Salkovskis (1985, 1989) draws a sharp distinction between unwanted intrusions and NATs in his cognitive--behavioral model of obsessions.
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Unfortunately most research on unwanted intrusive thoughts has not been clear on content, preferring instead to define the construct in terms of process characteristics alone. The result has been the development of intrusive thoughts measures that cut across a variety of negative thought content domains resulting in instruments with low discriminant validity (Clark, 1992). One solution is to recognize that unwanted intrusive thoughts, images, and impulses must be defined in terms of both process (that a thought is difficult to control and interrupts ongoing activity) and thought content. As will be seen from the discussion below, the tendency of researchers to focus exclusively on the form of the thought irrespective of its content has led to problems with many current measures of intrusive thoughts.
MEASURES OF INTRUSIVE THOUGHTS
Intrusive Thoughts Questionnaires A number of self-report questionnaires have been developed to assess the frequency of naturally occurring unwanted intrusive thoughts, images, and impulses. Most of these instruments also ask Ss to rate their intrusive thoughts on various appraisal or process characteristics such as controllability, unacceptability, discomfort, guilt, dismissability, unpleasantness and the like. However, one difficulty in evaluating the validity and reliability of these instruments is that none of the measures have been used extensively in research studies. Thus, a limited amount of psychometric information is available to determine their accuracy in assessing unwanted thought intrusions. Early questionnaires. Rachman and de Silva (1978) reported the first questionnaire developed to assess the frequency and ease of dismissability of unwanted obsessive-like intrusive thoughts and impulses. However, the authors provide very little psychometric information on the instrument, other than to indicate that 80% of nonclinical Ss reported at least one unwanted intrusion from the checklist. Salkovskis and Harrison (1984) adapted the Rachman and de Silva (1978) questionnaire by adding a rating on discomfort. They reported an internal reliability (coefficient ct) of 0.80 for the questionnaire, with 88% of 178 nonclinical Ss reporting at least one negative unwanted intrusive thought. More recently Salkovskis and colleagues included positive as well as negative unwanted thought intrusions on the questionnaire. Regression analysis revealed that high scores on the Beck Depression Inventory were significantly associated with the frequency of negative intrusive thoughts, whereas low scores on the Beck Anxiety Inventory were predictive of the frequency of positive thought intrusions (Reynolds & Salkovskis, 1991). In a second study, Reynolds and Salkovskis (1992) used their intrusive thoughts questionnaire to screen 54 nonclinical Ss for a subsequent experimental mood induction study. Unfortunately the authors did not report further psychometric data on the questionnaire in this article. We can conclude from this that although the intrusive thought questionnaire developed by Salkovskis and colleagues has been used successfully to identify Ss who report unwanted intrusive thoughts, insufficient psychometric information has been reported to comment on its validity or reliability. Intrusive Thoughts and Impulses Survey (ITIS). The 60-item ITIS (Niler & S. J. Beck, 1989) was based on items from Rachman and de Silva (1978). Each item described an unwanted thought (e.g. the thought that one had been poisoned) or impulse (e.g. to jump off a very high building). The thought or impulse in each item was rated in terms of frequency, dismissability, and distress. Of the 75 Ss who completed the ITIS, 99% reported experiencing intrusive thoughts or images. Gender did not correlate with any of the ITIS subscales except for the number of impulses endorsed. Correlations of 0.19-0.44 were found between the ITIS intrusive thoughts subscales and the State-Trait Anxiety Inventory--Trait Scale, Beck Depression Inventory, and Perceived Guilt Inventory. These low-to-moderate correlations with validated mood and symptom measures suggests some initial convergent validity for the ITIS. Unfortunately the instrument has not been utilized in any subsequent published study. Intrusive Thoughts Questionnaire (ITQ). With the ITQ (Edwards, 1985) Ss record their most unpleasant and pleasant intrusive thought and then rate each thought on 16 items assessing form, frequency, triggers, duration, control strategies, amount of distress or excitement, perceived controllability and acceptability. These items assess both process characteristics of intrusions and
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beliefs about the control and acceptability of unwanted intrusive thoughts. In addition, the negative intrusive thought is rated on 10 statements for amount of associated distress, and the positive intrusive thought is rated on 10 statements for amount of physiological arousal (Edwards & Dickerson, 1987a, 1987b). Factor analysis of the first 16 items of both the positive and negative scales resulted in a controllability dimension consisting of 4 items. A controllability scale based on this solution resulted in coefficient ~s of 0.86 and 0.88 for negative and positive intrusions, respectively. No other interpretable dimensions emerged from the factor analysis, although on a post hoc basis the authors constructed an acceptability scale consisting of 3 items with low to moderate inter-item correlations. The 10 distress statements for the negative intrusions were summed, yielding an internal consistency coefficient of 0.89. For the positive intrusion, the 10 physiological arousal statements were factor analyzed yielding two stable dimensions, distress and arousal. The only convergent validity data reported for these ITQ scales consisted of low to moderate correlations (rs = 0.20-0.28) with the POMS Depression Scale. Edwards and Dickerson (1987a) used the ITQ to identify Ss with a negative thought intrusion and found the negative intrusions took longer to replace than did neutral thoughts. Also research with the ITQ has shown that both positive and negative intrusions are uncontrollable, and that the attentional value and intensity of the intrusion is the best predictor of uncontrollability rather than degree of unpleasantness (Edwards & Dickerson, 1987b; England & Dickerson, 1988). Although the ITQ has provided some insights into the similarities between positive and negative thought intrusions, the instrument has not been adequately validated. The exclusive focus on individuals' single most pleasant and unpleasant intrusive thought is too restrictive. As a result the ITQ may not adequately assess the experience of unwanted intrusions in Ss who have many negative distressing thoughts. Also, the lack of factorial stability in the ITQ and the lack of convergent validity data raises questions about the construct validity of the ITQ. Distressing Thoughts Questionnaire (DTQ). The DTQ (Clark & de Silva, 1985) assesses 6 representative anxious thoughts and 6 depressive thoughts (e.g. thought of personal failure) along 5 appraisal dimensions; frequency, sadness, worry, removal, and disapproval. Frequency, sadness, worry, removal and disapproval scales were constructed by summing across the 6 depressive and anxious thought statements. These scales had adequate internal consistency (cts > 0.70; Clark & de Silva, 1985) and adequate 3 month test-retest reliability (rs from 0.53 to 0.90; Clark, 1992). In addition, the DTQ scales correlated with the STAI-State Scale (r = 0.23-0.62; Clark, 1992), the Eysenck Personality Questionnaire--Neuroticism Scale (r = 0.36-0.59; Clark & Hemsley, 1985), the Cognitive and Somatic subscales of the Cognitive-Somatic Anxiety Questionnaire (r = 0.33-0.57; Clark, 1992), and the Beck Depression Inventory (r = 0.31-0.79; Clark, 1992). These findings support the convergent validity of the DTQ scales. Two major problems, however, became evident with the DTQ. First, the DTQ scales were highly intercorrelated, suggesting that they may not be assessing different parameters of negative thinking but rather a single general distress or negative affect component. Second, the anxious thought statements, which were originally developed to assess unwanted obsessive-like intrusive thoughts, did not correlate highly with the Maudsley Obsessional-Compulsive Inventory (MOCI; r = 0.28-0.52; Clark, 1992) or with the Leyton Obsessional Inventory Trait Scale (r = 0.22; Clark, 1984). In fact, Clark (1992) found that only two DTQ thought statements, "thoughts of personally unacceptable sexual acts" and "thoughts of saying rude and/or unacceptable things to someone", represented unwanted obsessive-like intrusive thoughts. Cognitive Intrusions Questionnaire (CIQ). The CIQ (Freeston, 1990) consists of the 6 anxious thought statements from the DTQ (Clark & de Silva, 1985) and an open-ended question to assess any additional idiosyncratic intrusive thoughts (Edwards & Dickerson, 1987b). Subjects rate each thought statement endorsed on 13 appraisal dimensions; frequency, sadness, worry, removal, disapproval, guilt, belief, triggers, form (whether the intrusion was a thought, image, urge, impulse, doubt or feeling), thought removal strategies used and their success, discomfort reduction, and perceived responsibility. A fourteenth dimension represented the number of different intrusive statements endorsed by the Ss. Scales were constructed by summing across the 13 appraisal dimensions for each of the intrusive thoughts statements. In addition, Ss indicated which of 9 possible strategies they used to control their intrusive thoughts.
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Freeston, Ladouceur and colleagues have now conducted a number of studies using the CIQ. In the first study, using 125 French-Canadian university students (Freeston, Ladouceur, Thibodeau & Gagnon, 1991, 1992), 99% of the sample endorsed at least one intrusive thought item on the CIQ. Adequate internal consistency was found for each of the 7 intrusive thought scales (ors ranged from 0.68 for the verbal aggression item to 0.86 for the idiosyncratic intrusion). Cluster analysis based on Ss' response strategy scores proved unstable, so 3 response groups were defined according to their major response control strategy. Between-groups and within-Ss analyses were significant indicating that the CIQ was sensitive to differences in the way individuals appraise and respond to their unwanted intrusive thoughts. Factor analysis of the 14 dimensions of the CIQ resulted in 5 factors with eigenvalues greater than 1 (Freeston et al., 1992). Although the authors retained all 5 factors, this may have resulted in an overextracted solution. Factors 3 and 5 appear to be insignificant dimensions with only one or two items loading on each, Factors 1 and 2 accounted for most of the variance in the solution. Factor 1 was labeled severity (frequency, sadness, worry, removal and belief), Factor 2 was labelled evaluation (guilt, responsibility, disapproval), and Factor 4 was labelled diversity (number of forms, strategies and thoughts endorsed). The severity, evaluation, and diversity factor scores were more highly correlated with the Beck Anxiety and Depression Inventories (rs = 0.32-0.46) than with the Compulsive Activity Checklist (rs = 0.21-0.28). Hierarchical regression analysis indicated that the CIQ accounted for more variance in the measures of depression and anxiety than with the measure of compulsion. In a second study, the CIQ and other symptom measures were administered to 885 nonpsychiatric individuals in two hospital waiting rooms (Freeston & Ladouceur, 1993). Although the results of this study suggest the importance of distinguishing the ego-syntonic thoughts characteristic of worry from the ego-dystonic thoughts of obsessive-like intrusions, the failure to report correlations between the CIQ and the measures of worry and obsessions means that this study makes a limited contribution to establishing the psychometric status of the CIQ. Unlike other intrusive thoughts questionnaires, the CIQ has been administered to OCD patients. In one study, 21 OCD patients completed the CIQ, Beck Depression Inventory, Beck Anxiety Inventory, ratings of obsession frequency and discomfort, and daily ratings of mood when in a low mood and again when in a high mood (Freeston, Ledouceur, Rheaume, Letarte, Bujold, Thibodean, & Gagnon, 1992). The CIQ change score was highly correlated with the changes in the Beck Depression Inventory (r = 0.88) and changes in the Beck Anxiety Inventory (r = 0.76) but was unrelated to changes in patients' ratings of obsession frequency or severity (correlation coefficients for obsession frequency and severity were not reported in the paper). In summary, the CIQ has been used more extensively than any other self-report measure of unwanted intrusive thoughts. Despite the substantive findings obtained with this instrument, there are a number of problems that call into question the construct validity of the CIQ as a measure of obsessive-like intrusive thoughts. First, the high correlations between the CIQ and anxiety symptom measures as well as the low correlations with obsessional symptom measures suggests that the CIQ may have broader relevance for generalized anxiety symptoms as opposed to being more directly focused on obsessive compulsive symptoms. Second, the discriminant validity of the instrument has not been established. In particular it is unclear whether the CIQ measures different cognitive phenomena from what is assessed with anxious cognition questionnaires like the Cognitions Checklist (Beck et al., 1987) or worry measures such as the Penn State Worry Questionnaire (Meyer, Miller, Metzger & Borkovec, 1990) or Worry Domains Questionnaire (Tallis et al., 1992). Third, clarification of the factorial structure of the CIQ is needed to ensure that the 14 appraisal scales actually assess distinct parameters of cognition rather than a single general distress or severity dimension. Obsessional Intrusions Inventory (OII). Because previous self-report measures of unwanted intrusive thoughts failed to take into account the content of obsessional thinking, Purdon and Clark (1993) developed the 52-item OII to assess ego-dystonic thoughts, images, or impulses of violence, sex, accidents, dirt and contamination. In addition to obtaining a frequency rating on the 52 statements, Ss also rate their most upsetting negative thought intrusion on 7 appraisal dimensions (unpleasantness, upset, guilt, avoidance of triggers, uncontrollability, unacceptability, and belief that the intrusion might occur in real life) as well as 10 possible thought control strategies. In the
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revised OII (Purdon & Clark, 1994b), the rating on upset was dropped, and 4 new ratings were added to reflect concerns about control and responsibility for the unwanted intrusion. Two studies have been conducted using the OII or revised OII described in Purdon & Clark, 1993, 1994a, 1994b). In the first, 99 % of the sample endorsed at least one of the 52 intrusive thought statements (Purdon & Clark, 1993). Factor analysis of the 52 OII checklist items revealed a single dimension for men (labelled Sex/Aggression), but two dimensions, Sex/Aggression and Dirt/Contamination, for women (Purdon & Clark, 1993). Thus a single OII Total Scale was constructed for men with an ct of 0.93, whereas two total scales were derived for women, Sex/Aggression and Dirt/Contamination, with ~ coefficients of 0.88 and 0.82, respectively. Zero-order and partial correlations computed between the OII Total Scales and measures of depressive, anxious, and panic-related negative thoughts revealed that the OII Total Scales had a moderate relationship with anxious thinking (partial rs = 0.22-0.40) but was uncorrelated with depressive thinking (partial r s = -0.02-0.14). Regression analyses indicated that the OII total scale scores, compared to the other measures of thoughts, were uniquely predictive of self-reported obsessional symptoms but not anxious or depressive symptoms. To determine whether item overlap accounted for the strong correlation between the OII Total Scales and obsessional symptoms, as measured by the Padua Inventory, we excluded 9 items from the Padua that dealt with content similar to the OII (i.e. sex, aggression, dirt and contamination themes). The resulting correlation coefficients were practically identical to those reported in Purdon and Clark (1993). In a second study, Purdon and Clark (1994b) found that the OII Total Score, which assesses overall frequency of intrusions, was unrelated to worry disposition as measured by the Penn State Worry Questionnaire (r = 0.11). However the White Bear Suppression Inventory (Wegner & Zanakos, 1994), which measures one's tendency to suppress unwanted thoughts, had a low correlation with the OII Total scores (r = 0.22) but was moderately correlated with anxiety and depression measures (r = 0.49 and 0.41, respectively; Purdon & Clark, 1994b). This suggests that the White Bear Suppression Inventory may be more applicable to the experience of ego-syntonic than ego-dystonic thoughts. In sum, initial psychometric data tends to support the construct validity of the OII in nonclinical samples. The 52 thought statements on the OII are distinguishable from negative automatic thoughts and worry, and show a stronger association with obsessional than anxious or depressive symptoms. This suggests that the OII assesses the obsessive-like unwanted intrusive thoughts, which Rachman (1981) and others consider the basis of clinical obsessions. However the OII has not been administered to clinical samples so we have no information on the clinical utility of this instrument. Interview and diary assessment
Given the idiosyncratic nature of unwanted intrusive thoughts, one could argue that self-report questionnaires cannot adequately assess intrusions because they limit Ss' responses to a predetermined set of items. For this reason, interview and diary approaches may be more accurate by focusing on the specific intrusions unique to each individual. Only a few studies have interviewed Ss in order to assess their experience of unwanted intrusive thoughts (Freeston, Ladouceur, Provencher & Blais, 1993; Parkinson & Rachman, 1981a, 1981b; Rachman & de Silva; 1978). Typically the interviews are open-ended rather than structured. After eliciting a sample of unwanted intrusions, Ss are asked by the interviewer to rate their emotional reaction and appraisal of the intrusions on Likert-type scales. None of the studies have reported reliability data or inter-rater agreement using an interview approach. Furthermore, no convergent or discriminant validity data have been reported and no comparisons have been made between interview and retrospective self-report questionnaires. Although interviews may identify the idiosyncratic intrusions better than questionnaires do, the presence of an interviewer could influence whether or not Ss report highly unacceptable intrusive thoughts (e.g. those dealing with sex or violence). Thus there is no empirical evidence at this point to suggest that an interview approach is preferable to self-report questionnaires in the assessment of unwanted negative intrusive thoughts. In a recent study, Wells and Morrison (1994) had 30 students monitor 2 worries and 2 obsessions each day over a 2-week period. Subjects rated these cognitions on a number of appraisal dimensions
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using 0-100 scales, where high scores indicate greater amounts of the quality in question. Results suggest that Ss could reliably distinguish between worry and obsession, and that the 2 types of cognition are different on a number of appraisal dimensions. Given these findings, it would be interesting to compare a retrospective measure of intrusive thoughts and daily ratings of the cognitive phenomena.
Measures of responsibility and meta-cognitive beliefs Two constructs crucial to understanding the link between normal unwanted intrusive thoughts and clinical obsessions are (1) an exaggerated sense of personal responsibility; and (2) the existence of dysfunctional recta-cognitive beliefs (Clark & Purdon, 1993; Rachman, 1993; Salkovskis, 1985, 1989). Recently Salkovskis, Rachman, Ladouceur and Freeston defined exaggerated appraisal of responsibility as "the belief that one has power which is pivotal to bring about or prevent subjectively crucial negative outcomes" (cited in Salkovis, 1994, p. 11). The measurement of excessive responsibility has been most difficult because of the complex and multifaceted nature of the construct (see Rachman, 1993). As a result, single rating scales of perceived responsibility, such as found on the CIQ or OII, have met with only limited success in measuring this construct (Freeston et al., 1991, 1992; Purdon & Clark, 1994a, b). In response to this Rheaume, Ladouceur, Freeston and Letarte (1995) developed a multidimensional Responsibility Questionnaire (RQ) based on the newer operational definition of responsibility proposed by Salkovskis, Rachman, Ladouceur and Freeston. The RQ assesses severity, relevance, probability, influence, pivotal influence and responsibility across 14 situations. Initial results support the construct validity of the RQ, with the Responsibility Total Score showing a moderate correlation (r = 0.58) with self-reported obsessional symptoms in a nonclinical sample (Rheaume, Ladouceur, Freeston & Letarte, 1993). However, the Responsibility Total Score also had a low correlation with the CIQ (r = 0.28) and the Inventory of Beliefs Related to Obsessions (r = 0.16), which is contrary to the hypothesis that appraisals of responsibility are linked to unwanted intrusive thoughts. A final construct considered important in cognitive-behavioral theories of obsessions is that of dysfunctional beliefs or schemas about one's thoughts. Flavell (1979) referred to the tendency to monitor one's thoughts as metacognitive processing. There is little doubt that obsessional patients monitor their thinking meticulously and hold specific dysfunctional beliefs about the importance and need to control their thoughts. Thus, it is likely that certain dysfunctional beliefs about thought control, personal responsibility, the fusion of thought and action, and the consequences of unwanted intrusive thoughts will lead to greater effort at controlling one's intrusive thoughts (Clark & Purdon, 1993; Rachman, 1993; Salkovskis, 1994). However, measures of dysfunctional recta-cognitive beliefs are still in the developmental stage. Freeston, Ladouceur, Gagnon and Thibodeau (1993) developed the 20-item Inventory of Beliefs Related to Obsessions (IBRO) to assess beliefs about responsibility and the control of unwanted intrusive thoughts. Principle components analysis of the 20 items revealed 3 dimensions, with a large 1l-item first factor, labelled dysfunctional responsibility schema accounting for 19.6% of the variance. The second factor consisted of 5 items, which measured overestimation of threat. The third factor consisted of 4 items, which assessed intolerance of uncertainty. The IBRO Total Scale had adequate internal consistency (0t = 0.82) and adequate test-retest reliability (r = 0.70). The IBRO was moderately correlated with the Beck Anxiety Inventory (r = 0.40), and with a measure of general dysfunctional beliefs called the Belief Scale (r = 0.59). The IBRO was also moderately correlated with the Obsessive Thoughts Checklist (r = 0.47) and with the Padua Inventory (r = 0.39). Hierarchical regression analysis indicated that the IBRO accounted for a significant amount of variance in the Padua Total Score, and the Padua Inventory's Mental Control, Checking, and Contamination subscales, after partialling out the effects of negative affect. Freeston et al. (1993) compared IBRO scores of 3 groups of Ss: (1) obsessive compulsive patients; (2) nonclinical Ss who were more distressed than controls by their intrusive thoughts, and used escape-avoidance control strategies; and (3) normal controls. Groups 1 and 2 scored higher than controls on the IBRO Total Score. These findings suggest the IBRO is a promising instrument for assessing dysfunctional beliefs specifically related to unwanted intrusive thoughts. A possible limitation of the IBRO is that only 5 items deal directly with beliefs about the importance of
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controlling unwanted intrusive thoughts. We consider beliefs about thought control to be an important component of dysfunctional meta-cognitive obsessional beliefs (see Clark & Purdon, 1993). We are aware of 3 research groups currently working toward the development of self-report instruments to asses dysfunctional meta-cognitive beliefs. Cartwright and Wells (1994) have developed a 65-item Meta-Cognitions Questionnaire to assess beliefs associated with worrisome thoughts. Frost and Steketee (Frost, personal communication, November, 1994) are in the process of constructing a meta-cognitive beliefs inventory for obsessions, and we are currently working on an instrument called the Meta-Cognitive Beliefs Questionnaire designed to assess beliefs related to unwanted obsessive thoughts in normals. For the latter scale, a pool of 90 items were written to assess beliefs about the control of intrusive thoughts, consequences of intrusions, responsibility, fusion of thought and action, guilt, and positive characteristics of unwanted intrusive thoughts. Initial item analysis led to the deletion of a number of poor items, and we are in the process of conducting our first validation study of the instrument. CONCLUSIONS AND RECOMMENDATIONS On the basis of this review we draw the following conclusions and recommendations for the assessment of unwanted intrusive thoughts. 1. Measures of unwanted intrusive thoughts should be made more specific by assessing content and process characteristics. Instruments that have defined intrusive thoughts broadly by referring only to the unwillful nature of cognition (i.e. process only) have suffered from low discriminant validity. Defining unwanted intrusive thoughts more precisely by referring to both content and process characteristics will not only improve the discriminant validity of intrusive thoughts measures, but it will allow us to more accurately investigate the differentiation of cognition and affect. For example Beck's (1976, 1987) content-specificity hypothesis is based on the notion that negative automatic thoughts with different content are related to different psychopathological conditions (see also Beck et al., 1987). In addition, Wells and Morrison (1994) argue that understanding the difference between types of cognition is important in developing more precise information processing models of clinical phenomena such as worry. In sum, we do not believe it is possible to achieve the level of measurement accuracy demanded by current cognitive-clinical models without first redefining our cognitive constructs by considering both content and process. 2. Most research on the assessment of unwanted intrusive thoughts has not adequately considered the problem of discriminant validity. Thus, instruments that assess cognitive intrusions (which are considered an analogue to clinical obsessions) must have a stronger relationship with obsessional than anxious or depressive symptom measures. Intrusive thoughts measures which show nonspecificity will not be appropriate for cognitive research in OCD. 3. Instrusive thoughts measures must also show differentiation from measures of other cognitive phenomena such as worry and negative automatic anxious and depressive thoughts. To date, few studies have demonstrated specificity at this cognitive level. Given the similarities between obsessional intrusive thoughts and worry (Turner, Beidel & Stanley, 1992; Wells, 1994), it is crucial that obsessional intrusive thought measures be distinguishable from worry measures. 4. The idiosyncratic nature of unwanted intrusive thoughts poses a challenge for those using retrospective self-report questionnaires. It is important that these measures provide items that fully represent the range and breadth of intrusive thought content. This should be done prior to assessing the appraisal variables associated with one or two prominent intrusions. If this approach is not taken, then Ss may report on intrusive thoughts that have little personal meaning. Such thoughts are of much less interest, particularly if the aim of the research is to understand the escalation of normal intrusive thoughts into obsessions. Thus measures, such as the Revised Distressing Thoughts Questionnaire, which contain only a few items of relevance to obsessional intrusive thoughts are less adequate, particularly for individuals who experience frequent and varied unwanted intrusive thoughts. 5. Research is needed to compare different assessment methods for measuring unwanted intrusive thoughts. There are no published studies that have compared retrospective self-report questionnaires with diary assessment of intrusive thoughts. Studies comparing different assessment methods are essential for establishing construct validity of the measures.
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6. Most measures of unwanted intrusive thoughts do include ratings on a variety of appraisal variables. Although this is an important aspect of the assessment of intrusions, greater attention must be given to selecting a few distinct appraisal variables and constructing clear and specific ratings of each process variable. Some of the existing intrusive thoughts measures have produced unstable and complex factorial solutions, suggesting possible ambiguities in how the appraisal variables have been rated. 7. The constructs of personal responsibility and meta-cognitive beliefs are important to understanding the link between distressing intrusive thoughts and obsessions. New measures of these constructs must demonstrate sensitivity and specificity to obsessional symptoms and thinking in clinical and nonclinical samples in order to support their construct validity. 8. Finally several investigators have used indirect procedures such as information processing (Freeston, Ladouceur, Rheaume, Letarte, Gagnon & Thibodeau, 1994; Parkinson & Rachman, 198 l c) or psychophysiological measures (Clark, 1984) to investigate unwanted intrusive thoughts. Because the intrusion of unwanted cognitions into consciousness has an impact on attention, emotion and cognitive processing, information processing experiments can be used to investigate the presence of intrusive cognition. An important area of future research will be to investigate the concordance between information processing or psychophysiological effects of intrusive thoughts, and self-report or phenomenoiogical measures of unwanted intrusions. This research will be crucial for understanding not only the conceptual nature of intrusive thoughts, but for experimentally establishing the construct validity of self-report measures of unwanted intrusive cognitions. Acknowledgements--We are grateful to the Social Sciences and Humanities Research Council of Canada who awarded D. A. Clark a standard grant (grant no. 410-92-0427) and Christine Purdon a Doctoral Fellowship (grant no. 752-93-1434).
REFERENCES Barlow, D. H. (1988). Anxiety and its disorders: The nature and treatment of anxiety and panic. New York: Guildford Press. Beck, A. T. (1976). Cognitive therapy and the emotional disorders. New York: New American Library. Beck, A. T. (1987). Cognitive models of depression. Journal of Cognitive Psychotherapy, I, 2-27. Beck, A. T. & Clark, D. A. (1988). Anxiety and depression: an information processing perspective. Anxiety Research, 1, 23-36. Beck, A. T., Brown, G., Steer, R. A., Eidelson, J. I. & Riskind, J. H. (1987). Differentiating anxiety and depression utilizing the Cognitions Checklist. Journal of Abnormal Psychology, 96, 179-183. Cartwright, S. & Wells, A. (1994). Meta-Cognitions Questionnaire. Unpublished instrument, Department of Psychiatry, Warneford Hospital, Oxford University, Oxford, England. Clark, D. A. (1984). Psychophysiological, behavioural, and self-report investigations into cognitive-affective interaction within the context of potentially aversive ideation. P h . D . dissertation, Department of Psychology, Institute of Psychiatry, University of London. Clark, D. A. (1988). The validity of measures of cognition: A review of the literature. Cognitive Therapy and Research, 12, 1 20. Clark, D. A. (1992). Depressive, anxious and intrusive thoughts in psychiatric inpatients and outpatients. Behaviour and Research and Therapy, 30, 93-102. Clark, D. A. & de Silva, P. (1985). The nature of depressive and anxious thoughts: Distinct or uniform phenomena? Behaviour Research and Therapy, 23, 383-393. Clark, D. A. & Hemsley, D. R. (1985). Individual differences in the experience of depressive and anxious intrusive thoughts. Behaviour Research and Therapy, 23, 279-282. Clark, D. A. & Purdon, C. (1993). New perspectives for a cognitive theory of obsessions. Australian Psychologist, 28, 161-167. Davey, G. C. L. (1993), A comparison of three worry questionnaires. Behaviour Research and Therapy, 31, 51-56. Edwards, S. (1985). Intrusive thoughts. Unpublished Masters thesis. Department of Psychology, Australian National University. Edwards, S. & Dickerson, M. (1987a). Intrusive unwanted thoughts: a two-stage model of control. British Journal of Medical Psychology, 60, 317-328. Edwards, S. & Dickerson, M. (1987b). On the similarity of positive and negative intrusions. Behaviour Research and Therapy, 25, 207-211. England, S. L. & Dickerson, M. (1988). Intrusive thoughts; unpleasantness not the major cause of uncontrollability. Behaviour Research and Therapy, 26, 279-282. Flavell, J. H. (1979). Metacognition and cognitive monitoring. A new area of cognitive-developmental inquiry. American Psychologist, 34, 906-911. Foa, E. B., Steketee, G. & Rothbaum, B. O. (1989). Behavioral/cognitive conceptualizations of post-traumatic stress disorder. Behavior Therapy, 20, 155-176. Freeston, M. (1990). Les intrusions cognitives et leur relation aux symptomes anxieux, depresifs et compulsifs. Masters thesis, Department of Psychology, Laval University. Freeston, M. & Ladouceur, R. (1993). Appraisal of cognitive intrusions and response style: Replication and extension. Behaviour Research and Therapy, 31, 185-191.
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Freeston, M., Ladouceur, R., Thibodeau, N. & Gagnon, F. (1991). Cognitive intrusions in a non-clinical population--l. Response style, subjective experience, and appraisal. Behaviour Research and Therapy, 29, 585-597. Freeston, M., Ladouceur, R., Thibodeau, N. & Gagnon, F. (1992). Cognitive intrusions in a non-clinical population--II. Associations with depressive, anxious and compulsive symptoms. Behaviour Research and Therapy, 30, 263-271. Freeston, M., Ladouceur, R., Gagnon, F. & Thibodeau, N. (1993). Beliefs about obsessional thoughts. Journal of Psychopathology and Behavioral Assesment, 15, 1-21. Freeston, M., Ladouceur, R., Provencher, M. & Blais, F. (1993). Strategies used with intrusive thoughts: Context, appraisal, mood and efficacy. Poster presented at the 27th annual convention of the American Association for the Advancement of Behaviour Therapy, Atlanta, November. Freeston, M., Ladouceur, R., Rheaume, J., Letarte, H., Gagnon, F. & Thibodeau, F. (1994). Self report of obsessions and worry. Behaviour Research and Therapy, 32, 29-36. Freeston, M. H., Ladoucer, R., Rheaume, J., Letarte, H., Bujold, A., Thibodeau, N. & Gagnon, F. (1992). Mood, cognitive appraisal, daily life events and obsessional severity in OCD without overt compulsions. Paper presented at the Annual Meeting of the Association for the Advancement of Behavior Therapy, Boston, November. Grey, S. J. (1982). The reliability of content analysis in the quantification of certain categories of thoughts. Unpublished manuscript, Department of Psychology, Institute of Psychiatry, London, England. Hollon, S. D. & Kendall, P. C. (1980). Cognitive self-statements in depression: Development of an Automatic Thoughts Questionnaire. Cognitive Therapy and Research, 4, 383-395. Meyer, T. J., Miller, M. L., Metzger, R. L. & Borkovec, T. D. (1990). Development and validation of the Penn State Worry Questionnaire. Behaviour Research and Therapy, 28, 487-495, Niler, E. R. & Beck, S. J. (1989). The relationship among guilt, anxiety and obsessions in a normal population. Behaviour Research and Therapy, 27, 213-220. Parkinson, L. & Rachman, S. (1981a). Part II--The nature of intrusive thoughts. Advances in Behaviour Research and Therapy, 3, I01-110. Parkinson, L. & Rachman, S. (1981b). Part Ill--Intrusive thoughts: the effects of an uncontrived stress. Advances in Behaviour Research and Therapy, 3, 111 118. Parkinson, L. & Rachman, S. (1981c). Part IV--Speed of recovery from an uncontrived stress. Advances in Behaviour Research and Therapy, 3, 119-123. Purdon, C. & Clark, D. A. (1993). Obsessive intrusive thoughts in nonclinical subjects--Part I. Content and relation with depressive, anxious and obsessional symptoms. Behaviour Research and Therapy, 31, 713-720. Purdon, C. & Clark, D. A. (1994a). Obsessive intrusive thoughts in nonclinical subjects--Part II. Cognitive appraisal, emotional response and thought control strategies. Behaviour Research and Therapy, 32, 403-410. Purdon, C. & Clark, D. A. (1994b). Perceived control and appraisal of obsessional intrusive thoughts: A replication and extension. Cognitive-Behavioural Psychotherapy, 22, 269-285. Rachman, S. (1971). Obsessional ruminations. Behaviour Research and Therapy, 9, 229-235. Rachman, S. (1976). The modification of obsessions: a new formulation. Behaviour Research and Therapy, 14, 437-443. Rachman, S. (1981). Part l.--Unwanted intrusive cognitions. Advances in Behaviour Research and Therapy, 3, 89-99. Rachman, S. (1993). Obsessions, responsibility and guilt. Behaviour Research and Therapy, 31, 149-154. Rachman, S. & de Silva, P. (1978). Abnormal and normal obsessions. Behaviour Research and Therapy, 16, 233-248. Rachman, S. & Hodgson, R. J. (1980). Obsessions and compulsions. Englewood Cliffs, NJ Prentice-Hall. Reynolds, M. & Salkovskis, P. M. (1991). The relationship among guilt, dysphoria, anxiety and obsessions in a normal population: an attempted replication. Behaviour Research and Therapy, 30, 259-265. Reynolds, M. & Salkovskis, P. M. (1992). Comparison of positive and negative intrusive thoughts and experimental investigation of the differential effects of mood. Behaviour Research and Therapy, 30, 273-281. Rheaume, J., Ladouceur, R., Freeston, M. H. & Letarte, H. (1993). Inflated responsibility in OCD: Psychometric studies of a semi-idiographic measure. Unpublished manuscript, Larval University, Department of Psychology. Rheaume, J., Ladouceur, R., Freeston, M. H. & Letarte, H. (1995). Inflated responsibility in obsessive compulsive disorder: Validation of an operational definition. Behaviour Research and Therapy, 33, 159-169. Salkovskis, P. M. (1985). Obsessional-compulsive problems: a cognitive-behavioural analysis. Behaviour Research and Therapy, 23, 571-584. Salkovskis, P. M. (1989). Cognitive-behavioural factors and the persistence of intrusive thoughts in obsessional problems. Behaviour Research and Therapy, 27, 677-682. Salkovskis, P. M. (1994). Cognitive-behavioural approaches to the understanding of obsessional problems. Unpublished manuscript, Department of Psychiatry, University of Oxford. Salkovskis, P. M. & Harrison, J. (1984). Abnormal and normal obsessions--a replication. Behaviour Research and Therapy, 22, I-4. Tallis, F., Eysenck, M. & Matthews, A. (1992). A questionnaire for the measurement of nonpathological worry. Personality and Individual Differences, 13, 161-168. Tallis, F., Davey, G. C. L. & Bond, A. (1994). The Worry Domains Questionnaire. In Davey, G. C. L. & Tallis, F. (Eds), Worrying: Perspectives on theory, assessment and treatment (pp. 285-297). New York: Wiley. Turner, S. M., Beidel, D. C. & Stanley, M. A. (1992). Are obsessional thoughts and worry different cognitive phenomena? Clinical Psychology Review, 12, 257-270. Wegner, D. M. (1992). You can't always think what you want: Problems in the suppression of unwanted thoughts. In Zanna, M. (Ed.), Advances in experimental social psychology (Vol. 25, pp. 193-225). New York. Academic Press. Wegner, D. M. & Erber, R. (1993). Social foundations of mental control. In Wegner, D. M. & Pennebaker, J. W, (Eds), Handbook of mental control (pp. 35-56). Englewood Cliffs, N J: Prentice-Hall. Wegner, D. M. & Zanakos, S. (1994). Chronic thought suppression. Journal of Personality, 62, 615-640. Wells, A. (1994). Attention and the control of worry. In Davey, G. C. L. & Tallis, F. (Eds), Worrying: Perspectives on theory, assessment and treatment (pp. 91-114). New York: Wiley. Wells, A. & Morrison, A. P. (1994). Qualitative dimensions of normal worry and normal obsessions: A comparative study. Behaviour Research and Therapy, 32, 867-870. Wenzlaff, R. M., Wegner, D. M. & Roper, D. W. (1988). Depression and mental control: The resurgence of unwanted negative thoughts. Journal of Personality and Social Psychology, 55, 882-892.
0005-7967(95)00030-5
INVITED
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Behav. Res. Ther. Vol. 33, No. 8, pp. 967-976, 1995 Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0005-7967/95 $9.50 + 0.00
ESSAY
ASSESSMENT OF UNWANTED INTRUSIVE THOUGHTS: A REVIEW AND CRITIQUE OF THE LITERATURE DAVID A. CLARK and CHRISTINE L. PURDON Department of Psychology, University of New Brunswick, Bag Service No. 45444, Fredericton, New Brunswick, Canada E3B 6E4 (Received 10 January 1995)
Summary--In this paper we review the assessment and measurement of normal unwanted intrusive thoughts, images, and impulses that are considered the basis of clinical obsessions. After highlighting some difficulties with how the definition of cognitive intrusion has been applied to the development of assessment measures, we evaluate the construct validity of a number of retrospective self-report instruments such as the Intrusive Thoughts Questionnaire, Cognitive Intrusions Questionnaire, and Obsessional Intrusions Inventory, as well as interview and diary procedures. Measures of personal responsibility and meta-cognitive beliefs, which are still in the developmental phase, are also discussed. We conclude with a number of recommendations and areas of further research which would strengthen the construct validity of measures of intrusive thoughts and related constructs.
INTRODUCTION The sudden intrusion of unwanted or unwillful thoughts, images, or impulses is a frequent and natural occurrence within our stream of consciousness. In fact at times we seem almost helpless in our efforts to consciously control the content or direction of our thoughts (Wegner, 1992), as evidenced by the unwanted intrusion of a variety of mental events from a mundane tune or rhyme to a negative, possibly even digusting or abhorrent, thought or image. This intrusive quality of cognition may be a particularly adaptive aspect of human nature when it involves the spontaneous occurrence of positive cognitions associated with creativity, inspiration, problem solving, and relief from boredom leading to increased motivation for productive work and social interaction. (Salkovskis, 1989). In the last two decades, clinical psychologists have begun to empirically investigate the role of unwanted, distressing intrusive thoughts, images and impulses in the pathogenesis of a variety of psychopathological states, such as obsessive compulsive disorders (Rachman & Hodgson, 1980), depression (Wenzlaff, Wegner & Roper, 1988), post traumatic stress disorder (Foa, Steketee & Rothbaum, 1989), and generalized anxiety disorder (Barlow, 1988). More recently Wegner and others have investigated the intentional suppression of unwanted thoughts and the role such mental control efforts may play in the regulation of mood, behavior, and social interaction as well as psychopathology (Wegner, 1992; Wegner & Erber, 1993). The study of unwanted intrusive distressing thoughts is particularly important to current psychological theories of obsessive compulsive disorder (OCD). In a seminal monograph on the topic, Rachman (1981) defined unwanted intrusive thoughts as repetitive, unacceptable or unwanted thoughts, images or impulses that: (a) interrupt ongoing activity; (b) are attributed to an internal origin; (c) are difficult to control. Based on this definition, then, any mental phenomena that repeatedly intrudes into our mind against our will could be considered an unwanted intrusive thought. However, it is the negative, distressing cognitive intrusions that have been the primary focus of clinical researchers interested in the etiology and maintenance of obsessions. Rachman and de Silva (1978) first demonstrated that nonclinical Ss experience unwanted thoughts that are similar in form BRr 33/S~:~
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and content to clinical obsessions. Since then, a number of other studies have replicated this finding, showing that 80-99% of nonclinical Ss report unwanted and unacceptable intrusive thoughts, images, or impulses (Clark & de Silva, 1985; Edwards & Dickerson, 1987a; England & Dickerson, 1988; Freeston, Ladouceur, Thibodeau & Gagnon, 1991; Niler & Beck, 1989; Parkinson & Rachman, 1981a; Purdon & Clark, 1993; Salkovskis & Harrison, 1984). As a result, recent cognitive-behavioural theories of OCD suggest that clinical obsessions may have their origins in the unwanted ego-dystonic intrusive thoughts found in normals (Rachman, 1971, 1976; Rachman & Hodgson, 1980; Salkovskis, 1985, 1989). Because of pre-existing dysfunctional beliefs about the need to control unacceptable thoughts, and the tendency to misinterpret unwanted intrusive thoughts as an indication that they may be responsible for harm to themselves or others, the intrusions of obsession-prone individuals can escalate in frequency and severity to become clinical obsessions (Clark & Purdon, 1993; Rachman, 1993; Salkovskis, 1994). In this article we will examine the assessment of unwanted intrusive thoughts as it pertains to research on clinical obsessions. We discuss issues involving the definition of intrusive cognitions, the reliability and validity of various intrusive thoughts instruments, and recent developments in the measurement of personal responsibility and meta-cognitive beliefs, processes considered crucial in the pathogenesis of clinical obsessions. The focus of the paper is on assessment via retrospective self-report methodology rather than on the production of intrusive thoughts in experimental settings. Although the latter represents a promising area of research for understanding the uncontrollability of cognition, most of the research on obsessive intrusive thoughts has relied on self-report questionnaires or interview. D E F I N I T I O N OF U N W A N T E D INTRUSIONS The empirical investigation of cognitive constructs has proven to be particularly challenging for clinical researchers. The internal, private nature of cognition makes any evaluation of the validity of Ss' self-reports of their thoughts most difficult (Clark, 1988). One approach used by clinical researchers to increase the accuracy of their cognitive assessments is to focus on specific thought content. Examples include the Cognitions Checklist (Beck, Brown, Steer, Eidelson & Riskind, 1987) and Automatic Thoughts Questionnaire (Hollon & Kendall, 1980). These measures assess negative automatic thoughts of loss and failure or harm and danger associated with depression or anxiety, and thereby assess specific thoughts defined strictly in terms of their content domain (Beck, 1987; Beck & Clark, 1988). This same content orientation to measurement is evident in most self-report measures of worry (Davey, 1993; Tallis, Davey & Bond, 1994; Tallis, Eysenck & Matthews, 1992; Wells, 1994). We find a very different emphasis when we consider unwanted intrusive thoughts. Here the focus is not on specific thought content but rather on process characteristics. That is, any thought, image or impulse may be an unwanted intrusive thought as long as it satisfies the criteria of intrusiveness (Rachman, 1981; Grey, 1982). This process-oriented approach to defining unwanted intrusive thoughts assumes Ss can reliably and accurately discern intrusive from nonintrusive cognitions, once they are provided with a definition or description of the constructs. However, there is some evidence that Ss require examples of unwanted intrusive thoughts before they can distinguish their own cognitive intrusions (Edwards & Dickerson, 1987a; Parkinson, personal communication, 1983). This suggests that individuals may need to be provided with thought content as well as process characteristics (i.e. degree of intrusiveness, uncontrollability) before they can distinguish these cognitive phenomena in their own stream of consciousness. The importance of considering both thought content and process is evident when we attempt to distinguish between different types of cognitive phenomena such as negative automatic thoughts and unwanted intrusive thoughts. Salkovskis (1985) argues that the negative automatic thoughts (NATs) that Beck (1976, 1987) and others consider important in anxiety and depression are different from unwanted intrusive thoughts. NATs tend to be ego-syntonic, less intrusive, plausible, rational and more difficult to access, whereas obsessional intrusive thoughts tend to be ego-dystonic, highly intrusive and accessible, irrational and less plausible. As a result, Salkovskis (1985, 1989) draws a sharp distinction between unwanted intrusions and NATs in his cognitive--behavioral model of obsessions.
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Unfortunately most research on unwanted intrusive thoughts has not been clear on content, preferring instead to define the construct in terms of process characteristics alone. The result has been the development of intrusive thoughts measures that cut across a variety of negative thought content domains resulting in instruments with low discriminant validity (Clark, 1992). One solution is to recognize that unwanted intrusive thoughts, images, and impulses must be defined in terms of both process (that a thought is difficult to control and interrupts ongoing activity) and thought content. As will be seen from the discussion below, the tendency of researchers to focus exclusively on the form of the thought irrespective of its content has led to problems with many current measures of intrusive thoughts.
MEASURES OF INTRUSIVE THOUGHTS
Intrusive Thoughts Questionnaires A number of self-report questionnaires have been developed to assess the frequency of naturally occurring unwanted intrusive thoughts, images, and impulses. Most of these instruments also ask Ss to rate their intrusive thoughts on various appraisal or process characteristics such as controllability, unacceptability, discomfort, guilt, dismissability, unpleasantness and the like. However, one difficulty in evaluating the validity and reliability of these instruments is that none of the measures have been used extensively in research studies. Thus, a limited amount of psychometric information is available to determine their accuracy in assessing unwanted thought intrusions. Early questionnaires. Rachman and de Silva (1978) reported the first questionnaire developed to assess the frequency and ease of dismissability of unwanted obsessive-like intrusive thoughts and impulses. However, the authors provide very little psychometric information on the instrument, other than to indicate that 80% of nonclinical Ss reported at least one unwanted intrusion from the checklist. Salkovskis and Harrison (1984) adapted the Rachman and de Silva (1978) questionnaire by adding a rating on discomfort. They reported an internal reliability (coefficient ct) of 0.80 for the questionnaire, with 88% of 178 nonclinical Ss reporting at least one negative unwanted intrusive thought. More recently Salkovskis and colleagues included positive as well as negative unwanted thought intrusions on the questionnaire. Regression analysis revealed that high scores on the Beck Depression Inventory were significantly associated with the frequency of negative intrusive thoughts, whereas low scores on the Beck Anxiety Inventory were predictive of the frequency of positive thought intrusions (Reynolds & Salkovskis, 1991). In a second study, Reynolds and Salkovskis (1992) used their intrusive thoughts questionnaire to screen 54 nonclinical Ss for a subsequent experimental mood induction study. Unfortunately the authors did not report further psychometric data on the questionnaire in this article. We can conclude from this that although the intrusive thought questionnaire developed by Salkovskis and colleagues has been used successfully to identify Ss who report unwanted intrusive thoughts, insufficient psychometric information has been reported to comment on its validity or reliability. Intrusive Thoughts and Impulses Survey (ITIS). The 60-item ITIS (Niler & S. J. Beck, 1989) was based on items from Rachman and de Silva (1978). Each item described an unwanted thought (e.g. the thought that one had been poisoned) or impulse (e.g. to jump off a very high building). The thought or impulse in each item was rated in terms of frequency, dismissability, and distress. Of the 75 Ss who completed the ITIS, 99% reported experiencing intrusive thoughts or images. Gender did not correlate with any of the ITIS subscales except for the number of impulses endorsed. Correlations of 0.19-0.44 were found between the ITIS intrusive thoughts subscales and the State-Trait Anxiety Inventory--Trait Scale, Beck Depression Inventory, and Perceived Guilt Inventory. These low-to-moderate correlations with validated mood and symptom measures suggests some initial convergent validity for the ITIS. Unfortunately the instrument has not been utilized in any subsequent published study. Intrusive Thoughts Questionnaire (ITQ). With the ITQ (Edwards, 1985) Ss record their most unpleasant and pleasant intrusive thought and then rate each thought on 16 items assessing form, frequency, triggers, duration, control strategies, amount of distress or excitement, perceived controllability and acceptability. These items assess both process characteristics of intrusions and
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beliefs about the control and acceptability of unwanted intrusive thoughts. In addition, the negative intrusive thought is rated on 10 statements for amount of associated distress, and the positive intrusive thought is rated on 10 statements for amount of physiological arousal (Edwards & Dickerson, 1987a, 1987b). Factor analysis of the first 16 items of both the positive and negative scales resulted in a controllability dimension consisting of 4 items. A controllability scale based on this solution resulted in coefficient ~s of 0.86 and 0.88 for negative and positive intrusions, respectively. No other interpretable dimensions emerged from the factor analysis, although on a post hoc basis the authors constructed an acceptability scale consisting of 3 items with low to moderate inter-item correlations. The 10 distress statements for the negative intrusions were summed, yielding an internal consistency coefficient of 0.89. For the positive intrusion, the 10 physiological arousal statements were factor analyzed yielding two stable dimensions, distress and arousal. The only convergent validity data reported for these ITQ scales consisted of low to moderate correlations (rs = 0.20-0.28) with the POMS Depression Scale. Edwards and Dickerson (1987a) used the ITQ to identify Ss with a negative thought intrusion and found the negative intrusions took longer to replace than did neutral thoughts. Also research with the ITQ has shown that both positive and negative intrusions are uncontrollable, and that the attentional value and intensity of the intrusion is the best predictor of uncontrollability rather than degree of unpleasantness (Edwards & Dickerson, 1987b; England & Dickerson, 1988). Although the ITQ has provided some insights into the similarities between positive and negative thought intrusions, the instrument has not been adequately validated. The exclusive focus on individuals' single most pleasant and unpleasant intrusive thought is too restrictive. As a result the ITQ may not adequately assess the experience of unwanted intrusions in Ss who have many negative distressing thoughts. Also, the lack of factorial stability in the ITQ and the lack of convergent validity data raises questions about the construct validity of the ITQ. Distressing Thoughts Questionnaire (DTQ). The DTQ (Clark & de Silva, 1985) assesses 6 representative anxious thoughts and 6 depressive thoughts (e.g. thought of personal failure) along 5 appraisal dimensions; frequency, sadness, worry, removal, and disapproval. Frequency, sadness, worry, removal and disapproval scales were constructed by summing across the 6 depressive and anxious thought statements. These scales had adequate internal consistency (cts > 0.70; Clark & de Silva, 1985) and adequate 3 month test-retest reliability (rs from 0.53 to 0.90; Clark, 1992). In addition, the DTQ scales correlated with the STAI-State Scale (r = 0.23-0.62; Clark, 1992), the Eysenck Personality Questionnaire--Neuroticism Scale (r = 0.36-0.59; Clark & Hemsley, 1985), the Cognitive and Somatic subscales of the Cognitive-Somatic Anxiety Questionnaire (r = 0.33-0.57; Clark, 1992), and the Beck Depression Inventory (r = 0.31-0.79; Clark, 1992). These findings support the convergent validity of the DTQ scales. Two major problems, however, became evident with the DTQ. First, the DTQ scales were highly intercorrelated, suggesting that they may not be assessing different parameters of negative thinking but rather a single general distress or negative affect component. Second, the anxious thought statements, which were originally developed to assess unwanted obsessive-like intrusive thoughts, did not correlate highly with the Maudsley Obsessional-Compulsive Inventory (MOCI; r = 0.28-0.52; Clark, 1992) or with the Leyton Obsessional Inventory Trait Scale (r = 0.22; Clark, 1984). In fact, Clark (1992) found that only two DTQ thought statements, "thoughts of personally unacceptable sexual acts" and "thoughts of saying rude and/or unacceptable things to someone", represented unwanted obsessive-like intrusive thoughts. Cognitive Intrusions Questionnaire (CIQ). The CIQ (Freeston, 1990) consists of the 6 anxious thought statements from the DTQ (Clark & de Silva, 1985) and an open-ended question to assess any additional idiosyncratic intrusive thoughts (Edwards & Dickerson, 1987b). Subjects rate each thought statement endorsed on 13 appraisal dimensions; frequency, sadness, worry, removal, disapproval, guilt, belief, triggers, form (whether the intrusion was a thought, image, urge, impulse, doubt or feeling), thought removal strategies used and their success, discomfort reduction, and perceived responsibility. A fourteenth dimension represented the number of different intrusive statements endorsed by the Ss. Scales were constructed by summing across the 13 appraisal dimensions for each of the intrusive thoughts statements. In addition, Ss indicated which of 9 possible strategies they used to control their intrusive thoughts.
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Freeston, Ladouceur and colleagues have now conducted a number of studies using the CIQ. In the first study, using 125 French-Canadian university students (Freeston, Ladouceur, Thibodeau & Gagnon, 1991, 1992), 99% of the sample endorsed at least one intrusive thought item on the CIQ. Adequate internal consistency was found for each of the 7 intrusive thought scales (ors ranged from 0.68 for the verbal aggression item to 0.86 for the idiosyncratic intrusion). Cluster analysis based on Ss' response strategy scores proved unstable, so 3 response groups were defined according to their major response control strategy. Between-groups and within-Ss analyses were significant indicating that the CIQ was sensitive to differences in the way individuals appraise and respond to their unwanted intrusive thoughts. Factor analysis of the 14 dimensions of the CIQ resulted in 5 factors with eigenvalues greater than 1 (Freeston et al., 1992). Although the authors retained all 5 factors, this may have resulted in an overextracted solution. Factors 3 and 5 appear to be insignificant dimensions with only one or two items loading on each, Factors 1 and 2 accounted for most of the variance in the solution. Factor 1 was labeled severity (frequency, sadness, worry, removal and belief), Factor 2 was labelled evaluation (guilt, responsibility, disapproval), and Factor 4 was labelled diversity (number of forms, strategies and thoughts endorsed). The severity, evaluation, and diversity factor scores were more highly correlated with the Beck Anxiety and Depression Inventories (rs = 0.32-0.46) than with the Compulsive Activity Checklist (rs = 0.21-0.28). Hierarchical regression analysis indicated that the CIQ accounted for more variance in the measures of depression and anxiety than with the measure of compulsion. In a second study, the CIQ and other symptom measures were administered to 885 nonpsychiatric individuals in two hospital waiting rooms (Freeston & Ladouceur, 1993). Although the results of this study suggest the importance of distinguishing the ego-syntonic thoughts characteristic of worry from the ego-dystonic thoughts of obsessive-like intrusions, the failure to report correlations between the CIQ and the measures of worry and obsessions means that this study makes a limited contribution to establishing the psychometric status of the CIQ. Unlike other intrusive thoughts questionnaires, the CIQ has been administered to OCD patients. In one study, 21 OCD patients completed the CIQ, Beck Depression Inventory, Beck Anxiety Inventory, ratings of obsession frequency and discomfort, and daily ratings of mood when in a low mood and again when in a high mood (Freeston, Ledouceur, Rheaume, Letarte, Bujold, Thibodean, & Gagnon, 1992). The CIQ change score was highly correlated with the changes in the Beck Depression Inventory (r = 0.88) and changes in the Beck Anxiety Inventory (r = 0.76) but was unrelated to changes in patients' ratings of obsession frequency or severity (correlation coefficients for obsession frequency and severity were not reported in the paper). In summary, the CIQ has been used more extensively than any other self-report measure of unwanted intrusive thoughts. Despite the substantive findings obtained with this instrument, there are a number of problems that call into question the construct validity of the CIQ as a measure of obsessive-like intrusive thoughts. First, the high correlations between the CIQ and anxiety symptom measures as well as the low correlations with obsessional symptom measures suggests that the CIQ may have broader relevance for generalized anxiety symptoms as opposed to being more directly focused on obsessive compulsive symptoms. Second, the discriminant validity of the instrument has not been established. In particular it is unclear whether the CIQ measures different cognitive phenomena from what is assessed with anxious cognition questionnaires like the Cognitions Checklist (Beck et al., 1987) or worry measures such as the Penn State Worry Questionnaire (Meyer, Miller, Metzger & Borkovec, 1990) or Worry Domains Questionnaire (Tallis et al., 1992). Third, clarification of the factorial structure of the CIQ is needed to ensure that the 14 appraisal scales actually assess distinct parameters of cognition rather than a single general distress or severity dimension. Obsessional Intrusions Inventory (OII). Because previous self-report measures of unwanted intrusive thoughts failed to take into account the content of obsessional thinking, Purdon and Clark (1993) developed the 52-item OII to assess ego-dystonic thoughts, images, or impulses of violence, sex, accidents, dirt and contamination. In addition to obtaining a frequency rating on the 52 statements, Ss also rate their most upsetting negative thought intrusion on 7 appraisal dimensions (unpleasantness, upset, guilt, avoidance of triggers, uncontrollability, unacceptability, and belief that the intrusion might occur in real life) as well as 10 possible thought control strategies. In the
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revised OII (Purdon & Clark, 1994b), the rating on upset was dropped, and 4 new ratings were added to reflect concerns about control and responsibility for the unwanted intrusion. Two studies have been conducted using the OII or revised OII described in Purdon & Clark, 1993, 1994a, 1994b). In the first, 99 % of the sample endorsed at least one of the 52 intrusive thought statements (Purdon & Clark, 1993). Factor analysis of the 52 OII checklist items revealed a single dimension for men (labelled Sex/Aggression), but two dimensions, Sex/Aggression and Dirt/Contamination, for women (Purdon & Clark, 1993). Thus a single OII Total Scale was constructed for men with an ct of 0.93, whereas two total scales were derived for women, Sex/Aggression and Dirt/Contamination, with ~ coefficients of 0.88 and 0.82, respectively. Zero-order and partial correlations computed between the OII Total Scales and measures of depressive, anxious, and panic-related negative thoughts revealed that the OII Total Scales had a moderate relationship with anxious thinking (partial rs = 0.22-0.40) but was uncorrelated with depressive thinking (partial r s = -0.02-0.14). Regression analyses indicated that the OII total scale scores, compared to the other measures of thoughts, were uniquely predictive of self-reported obsessional symptoms but not anxious or depressive symptoms. To determine whether item overlap accounted for the strong correlation between the OII Total Scales and obsessional symptoms, as measured by the Padua Inventory, we excluded 9 items from the Padua that dealt with content similar to the OII (i.e. sex, aggression, dirt and contamination themes). The resulting correlation coefficients were practically identical to those reported in Purdon and Clark (1993). In a second study, Purdon and Clark (1994b) found that the OII Total Score, which assesses overall frequency of intrusions, was unrelated to worry disposition as measured by the Penn State Worry Questionnaire (r = 0.11). However the White Bear Suppression Inventory (Wegner & Zanakos, 1994), which measures one's tendency to suppress unwanted thoughts, had a low correlation with the OII Total scores (r = 0.22) but was moderately correlated with anxiety and depression measures (r = 0.49 and 0.41, respectively; Purdon & Clark, 1994b). This suggests that the White Bear Suppression Inventory may be more applicable to the experience of ego-syntonic than ego-dystonic thoughts. In sum, initial psychometric data tends to support the construct validity of the OII in nonclinical samples. The 52 thought statements on the OII are distinguishable from negative automatic thoughts and worry, and show a stronger association with obsessional than anxious or depressive symptoms. This suggests that the OII assesses the obsessive-like unwanted intrusive thoughts, which Rachman (1981) and others consider the basis of clinical obsessions. However the OII has not been administered to clinical samples so we have no information on the clinical utility of this instrument. Interview and diary assessment
Given the idiosyncratic nature of unwanted intrusive thoughts, one could argue that self-report questionnaires cannot adequately assess intrusions because they limit Ss' responses to a predetermined set of items. For this reason, interview and diary approaches may be more accurate by focusing on the specific intrusions unique to each individual. Only a few studies have interviewed Ss in order to assess their experience of unwanted intrusive thoughts (Freeston, Ladouceur, Provencher & Blais, 1993; Parkinson & Rachman, 1981a, 1981b; Rachman & de Silva; 1978). Typically the interviews are open-ended rather than structured. After eliciting a sample of unwanted intrusions, Ss are asked by the interviewer to rate their emotional reaction and appraisal of the intrusions on Likert-type scales. None of the studies have reported reliability data or inter-rater agreement using an interview approach. Furthermore, no convergent or discriminant validity data have been reported and no comparisons have been made between interview and retrospective self-report questionnaires. Although interviews may identify the idiosyncratic intrusions better than questionnaires do, the presence of an interviewer could influence whether or not Ss report highly unacceptable intrusive thoughts (e.g. those dealing with sex or violence). Thus there is no empirical evidence at this point to suggest that an interview approach is preferable to self-report questionnaires in the assessment of unwanted negative intrusive thoughts. In a recent study, Wells and Morrison (1994) had 30 students monitor 2 worries and 2 obsessions each day over a 2-week period. Subjects rated these cognitions on a number of appraisal dimensions
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using 0-100 scales, where high scores indicate greater amounts of the quality in question. Results suggest that Ss could reliably distinguish between worry and obsession, and that the 2 types of cognition are different on a number of appraisal dimensions. Given these findings, it would be interesting to compare a retrospective measure of intrusive thoughts and daily ratings of the cognitive phenomena.
Measures of responsibility and meta-cognitive beliefs Two constructs crucial to understanding the link between normal unwanted intrusive thoughts and clinical obsessions are (1) an exaggerated sense of personal responsibility; and (2) the existence of dysfunctional recta-cognitive beliefs (Clark & Purdon, 1993; Rachman, 1993; Salkovskis, 1985, 1989). Recently Salkovskis, Rachman, Ladouceur and Freeston defined exaggerated appraisal of responsibility as "the belief that one has power which is pivotal to bring about or prevent subjectively crucial negative outcomes" (cited in Salkovis, 1994, p. 11). The measurement of excessive responsibility has been most difficult because of the complex and multifaceted nature of the construct (see Rachman, 1993). As a result, single rating scales of perceived responsibility, such as found on the CIQ or OII, have met with only limited success in measuring this construct (Freeston et al., 1991, 1992; Purdon & Clark, 1994a, b). In response to this Rheaume, Ladouceur, Freeston and Letarte (1995) developed a multidimensional Responsibility Questionnaire (RQ) based on the newer operational definition of responsibility proposed by Salkovskis, Rachman, Ladouceur and Freeston. The RQ assesses severity, relevance, probability, influence, pivotal influence and responsibility across 14 situations. Initial results support the construct validity of the RQ, with the Responsibility Total Score showing a moderate correlation (r = 0.58) with self-reported obsessional symptoms in a nonclinical sample (Rheaume, Ladouceur, Freeston & Letarte, 1993). However, the Responsibility Total Score also had a low correlation with the CIQ (r = 0.28) and the Inventory of Beliefs Related to Obsessions (r = 0.16), which is contrary to the hypothesis that appraisals of responsibility are linked to unwanted intrusive thoughts. A final construct considered important in cognitive-behavioral theories of obsessions is that of dysfunctional beliefs or schemas about one's thoughts. Flavell (1979) referred to the tendency to monitor one's thoughts as metacognitive processing. There is little doubt that obsessional patients monitor their thinking meticulously and hold specific dysfunctional beliefs about the importance and need to control their thoughts. Thus, it is likely that certain dysfunctional beliefs about thought control, personal responsibility, the fusion of thought and action, and the consequences of unwanted intrusive thoughts will lead to greater effort at controlling one's intrusive thoughts (Clark & Purdon, 1993; Rachman, 1993; Salkovskis, 1994). However, measures of dysfunctional recta-cognitive beliefs are still in the developmental stage. Freeston, Ladouceur, Gagnon and Thibodeau (1993) developed the 20-item Inventory of Beliefs Related to Obsessions (IBRO) to assess beliefs about responsibility and the control of unwanted intrusive thoughts. Principle components analysis of the 20 items revealed 3 dimensions, with a large 1l-item first factor, labelled dysfunctional responsibility schema accounting for 19.6% of the variance. The second factor consisted of 5 items, which measured overestimation of threat. The third factor consisted of 4 items, which assessed intolerance of uncertainty. The IBRO Total Scale had adequate internal consistency (0t = 0.82) and adequate test-retest reliability (r = 0.70). The IBRO was moderately correlated with the Beck Anxiety Inventory (r = 0.40), and with a measure of general dysfunctional beliefs called the Belief Scale (r = 0.59). The IBRO was also moderately correlated with the Obsessive Thoughts Checklist (r = 0.47) and with the Padua Inventory (r = 0.39). Hierarchical regression analysis indicated that the IBRO accounted for a significant amount of variance in the Padua Total Score, and the Padua Inventory's Mental Control, Checking, and Contamination subscales, after partialling out the effects of negative affect. Freeston et al. (1993) compared IBRO scores of 3 groups of Ss: (1) obsessive compulsive patients; (2) nonclinical Ss who were more distressed than controls by their intrusive thoughts, and used escape-avoidance control strategies; and (3) normal controls. Groups 1 and 2 scored higher than controls on the IBRO Total Score. These findings suggest the IBRO is a promising instrument for assessing dysfunctional beliefs specifically related to unwanted intrusive thoughts. A possible limitation of the IBRO is that only 5 items deal directly with beliefs about the importance of
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controlling unwanted intrusive thoughts. We consider beliefs about thought control to be an important component of dysfunctional meta-cognitive obsessional beliefs (see Clark & Purdon, 1993). We are aware of 3 research groups currently working toward the development of self-report instruments to asses dysfunctional meta-cognitive beliefs. Cartwright and Wells (1994) have developed a 65-item Meta-Cognitions Questionnaire to assess beliefs associated with worrisome thoughts. Frost and Steketee (Frost, personal communication, November, 1994) are in the process of constructing a meta-cognitive beliefs inventory for obsessions, and we are currently working on an instrument called the Meta-Cognitive Beliefs Questionnaire designed to assess beliefs related to unwanted obsessive thoughts in normals. For the latter scale, a pool of 90 items were written to assess beliefs about the control of intrusive thoughts, consequences of intrusions, responsibility, fusion of thought and action, guilt, and positive characteristics of unwanted intrusive thoughts. Initial item analysis led to the deletion of a number of poor items, and we are in the process of conducting our first validation study of the instrument. CONCLUSIONS AND RECOMMENDATIONS On the basis of this review we draw the following conclusions and recommendations for the assessment of unwanted intrusive thoughts. 1. Measures of unwanted intrusive thoughts should be made more specific by assessing content and process characteristics. Instruments that have defined intrusive thoughts broadly by referring only to the unwillful nature of cognition (i.e. process only) have suffered from low discriminant validity. Defining unwanted intrusive thoughts more precisely by referring to both content and process characteristics will not only improve the discriminant validity of intrusive thoughts measures, but it will allow us to more accurately investigate the differentiation of cognition and affect. For example Beck's (1976, 1987) content-specificity hypothesis is based on the notion that negative automatic thoughts with different content are related to different psychopathological conditions (see also Beck et al., 1987). In addition, Wells and Morrison (1994) argue that understanding the difference between types of cognition is important in developing more precise information processing models of clinical phenomena such as worry. In sum, we do not believe it is possible to achieve the level of measurement accuracy demanded by current cognitive-clinical models without first redefining our cognitive constructs by considering both content and process. 2. Most research on the assessment of unwanted intrusive thoughts has not adequately considered the problem of discriminant validity. Thus, instruments that assess cognitive intrusions (which are considered an analogue to clinical obsessions) must have a stronger relationship with obsessional than anxious or depressive symptom measures. Intrusive thoughts measures which show nonspecificity will not be appropriate for cognitive research in OCD. 3. Instrusive thoughts measures must also show differentiation from measures of other cognitive phenomena such as worry and negative automatic anxious and depressive thoughts. To date, few studies have demonstrated specificity at this cognitive level. Given the similarities between obsessional intrusive thoughts and worry (Turner, Beidel & Stanley, 1992; Wells, 1994), it is crucial that obsessional intrusive thought measures be distinguishable from worry measures. 4. The idiosyncratic nature of unwanted intrusive thoughts poses a challenge for those using retrospective self-report questionnaires. It is important that these measures provide items that fully represent the range and breadth of intrusive thought content. This should be done prior to assessing the appraisal variables associated with one or two prominent intrusions. If this approach is not taken, then Ss may report on intrusive thoughts that have little personal meaning. Such thoughts are of much less interest, particularly if the aim of the research is to understand the escalation of normal intrusive thoughts into obsessions. Thus measures, such as the Revised Distressing Thoughts Questionnaire, which contain only a few items of relevance to obsessional intrusive thoughts are less adequate, particularly for individuals who experience frequent and varied unwanted intrusive thoughts. 5. Research is needed to compare different assessment methods for measuring unwanted intrusive thoughts. There are no published studies that have compared retrospective self-report questionnaires with diary assessment of intrusive thoughts. Studies comparing different assessment methods are essential for establishing construct validity of the measures.
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6. Most measures of unwanted intrusive thoughts do include ratings on a variety of appraisal variables. Although this is an important aspect of the assessment of intrusions, greater attention must be given to selecting a few distinct appraisal variables and constructing clear and specific ratings of each process variable. Some of the existing intrusive thoughts measures have produced unstable and complex factorial solutions, suggesting possible ambiguities in how the appraisal variables have been rated. 7. The constructs of personal responsibility and meta-cognitive beliefs are important to understanding the link between distressing intrusive thoughts and obsessions. New measures of these constructs must demonstrate sensitivity and specificity to obsessional symptoms and thinking in clinical and nonclinical samples in order to support their construct validity. 8. Finally several investigators have used indirect procedures such as information processing (Freeston, Ladouceur, Rheaume, Letarte, Gagnon & Thibodeau, 1994; Parkinson & Rachman, 198 l c) or psychophysiological measures (Clark, 1984) to investigate unwanted intrusive thoughts. Because the intrusion of unwanted cognitions into consciousness has an impact on attention, emotion and cognitive processing, information processing experiments can be used to investigate the presence of intrusive cognition. An important area of future research will be to investigate the concordance between information processing or psychophysiological effects of intrusive thoughts, and self-report or phenomenoiogical measures of unwanted intrusions. This research will be crucial for understanding not only the conceptual nature of intrusive thoughts, but for experimentally establishing the construct validity of self-report measures of unwanted intrusive cognitions. Acknowledgements--We are grateful to the Social Sciences and Humanities Research Council of Canada who awarded D. A. Clark a standard grant (grant no. 410-92-0427) and Christine Purdon a Doctoral Fellowship (grant no. 752-93-1434).
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