The relationship between miscellaneous symptoms and major symptom factors in obsessive-compulsive disorder

Behaviour Research and Therapy 42 (2004) 1453–1467 www.elsevier.com/locate/brat

The relationship between miscellaneous symptoms and major symptom factors in obsessive-compulsive disorder Laura J. Summerfeldt a,b,
, Patricia H. Kloosterman a, Martin M. Antony b, Margaret A. Richter c, Richard P. Swinson b a

Department of Psychology, Trent University, Peterborough, Ont K9J 7B8, Canada Anxiety Treatment and Research Centre, St. Joseph’s Healthcare, and Department of Psychiatry and Behavioural Neurosciences, McMaster University, Canada c Anxiety Disorders Clinic, Centre for Addiction and Mental Health, and Department of Psychiatry, University of Toronto, Toronto, Canada

b

Received 1 April 2003; received in revised form 29 August 2003; accepted 26 September 2003

Abstract The diverse symptomatology of obsessive-compulsive disorder (OCD) is being increasingly regarded as reducible to a few symptom dimensions. However, prevailing factor-analytically derived models of symptom structure omit a number of the well-recognized ‘‘miscellaneous’’ symptoms of OCD. This study sought to determine whether miscellaneous OCD symptoms, ascertained by the Yale-Brown ObsessiveCompulsive Scale symptom checklist, could be differentially and reliably predicted by four symptom factors (obsessions and checking, symmetry and ordering, contamination and cleaning, and hoarding) in two independent groups of individuals with OCD (n = 381 and n = 107). Logistic regression analyses were used to determine the association of each of the miscellaneous symptoms with the symptom factors; then a single confirmatory factor analysis was conducted to test the model of associations in the smaller sample. Sixteen (89%) of the 18 symptoms examined were reliably predicted by one (11 items) or two (5 items) of the factors, with obsessions and checking and symmetry and ordering emerging as foremost predictors. The expanded four-factor model showed good fit with data from the second sample. Results are conceptually meaningful, but suggest the inadequacy of groupings based solely upon overt behaviors. These findings may aid clinical understanding of OCD and be of value to studies using symptom factors to guide investigation of its causes and correlates. # 2003 Elsevier Ltd. All rights reserved. Keywords: Obsessive-compulsive disorder; Miscellaneous; Symptoms; Factor analysis; Subtype




Corresponding author. Tel.: +1-705-748-1011 ex. 1526; fax: +1-705-748-1580. E-mail address: [email protected] (L.J. Summerfeldt).

0005-7967/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.brat.2003.09.006

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The strikingly diverse symptomatology of obsessive-compulsive disorder (OCD) is being increasingly regarded as reducible to a few symptom dimensions. In the past decade, several studies have used factor-analytic methods to systematically examine the structural characteristics of large arrays of OCD symptoms (Baer, 1994; Leckman et al., 1997; Mataix-Cols, Rauch, Manzo, Jenike, & Baer, 1999; Summerfeldt, Richter, Antony, & Swinson, 1999). Although there are potentially important differences in the models obtained, findings have converged upon variations on between three and five factorial themes, comprising symmetry and ordering, contamination and cleaning, obsessions and checking (potentially further divisible into harm-related obsessions and checking and other obsessions), and hoarding. Recent reviews have suggested that these symptom factors may be key to the understanding of the etiology of the disorder (e.g., Leckman, Zhang, Alsobrook, & Pauls, 2001; Nestadt et al., 2002; Pato, Pato, & Pauls, 2002), and findings substantiating this are beginning to appear in the literature (e.g., MataixCols, Rauch, Manzo, Jenike & Baer, 1999, 2002; Rauch et al., 1998). It is worth noting, however, that prevailing factor-analytic models of symptom structure leave out a number of the less easily categorized but well-recognized ‘‘miscellaneous’’ symptoms seen in OCD. This omission is not inconsequential. In the symptom checklist of the Yale-Brown Obsessive Compulsive Scale (Y-BOCS; Goodman et al., 1989), the most comprehensive and widely used inventory available and the source of data for these models, miscellaneous obsessions and compulsions represent over one quarter of the OCD symptoms ascertained. Despite this, they have been routinely omitted from analyses of symptom structure, and their pattern and degree of association with primary symptom factors has not been well established. To date, two published studies of empirically based OCD symptom subtypes have investigated their relationship with miscellaneous symptoms. Calamari, Wiegartz and Janeck (1999) included the miscellaneous categories of the Y-BOCS in a cluster analysis used to identify symptom-based groupings of 106 patients with OCD. The ‘‘obsessionals’’ grouping that included miscellaneous symptoms also showed elevated levels of aggressive obsessions, and checking and repeating compulsions. Though suggestive, the methodology used makes it difficult to extrapolate these findings to mainstream factor-analytically based models. More importantly, item-level analyses were not performed: All 13 a priori Y-BOCS symptom categories, including miscellaneous ones, were assigned a single score based on presence, absence, or current clinical dominance of at least one item in the category. Both these issues were addressed in the other existing study. Leckman et al. (1997) excluded miscellaneous category items from their factor analysis of OCD symptoms, but subsequently conducted a series of analyses to determine the associations of their four factors with the presence or absence of each of 22 Y-BOCS miscellaneous symptom items. Five reliable relationships were found, all with one of two factors. One miscellaneous obsession, fear of saying certain things, and two compulsions, need to tell, ask, or confess, and measures (not checking) to prevent harm or terrible consequences, were associated with higher scores on the obsessions and checking factor. Two miscellaneous symptoms were associated with the symmetry and ordering factor: Fear of not saying just the right thing, and touching and tapping compulsions. In interpreting Leckman et al.’s results, it should be noted that it is unclear both how factor scores were calculated for the analyses, and exactly what analyses were performed. Nonetheless, the findings are conceptually meaningful, and implicate two symptom

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dimensions—obsessions and checking and symmetry and ordering—as chief predictors of several miscellaneous symptoms. Findings from another body of literature provide additional support for the likely centrality of these symptom dimensions. Miscellaneous symptoms have received particular attention in research on tic-related OCD. Indeed, in one study comparing symptom profiles of patients with OCD and Tourette’s disorder versus OCD alone, 70 percent of the differentiating symptoms found to be elevated in the former group were from the miscellaneous categories of the YBOCS symptom checklist (Miguel et al., 1997). Several such studies have yielded similar results, with tic-related OCD most commonly linked with such miscellaneous obsessions as intrusive nonviolent images and sounds, and compulsive touching and tapping, and blinking and staring; importantly, these often accompany aggressive and other obsessions and symmetry-related symptoms (George, Trimble, Ring, Sallee, & Robertson, 1993; Holzer et al., 1994; Leckman et al., 1997; Miguel et al., 1997; Petter, Richter, & Sandor, 1998; see also Cath et al., 2001). Clearly, understanding of the associations among the many currently uncategorized miscellaneous symptoms of OCD and established symptom dimensions would aid efforts to characterize and understand the disorder and its phenotypes. Existing studies point to the likely importance of two symptom factors–obsessions and checking, and symmetry and ordering. However, the results of the one item-level study to date, by Leckman et al. (1997), have not been replicated. More importantly, this study found significant associations for only a portion of the miscellaneous symptoms examined: the relationship among symptom dimensions and the majority of recognized miscellaneous symptoms remains unknown. The purpose of the present study was to determine the associations of a number of recognized miscellaneous symptoms of OCD to established OCD symptom factors—obsessions and checking, symmetry and ordering, contamination and cleaning, and hoarding (Leckman et al., 1997)—using robust multivariate statistical methods and data from samples of sufficient size to withstand several difficulties posed by symptom data. Our analyses proceeded in two stages. In the first stage, we sought to determine a model of associations in a large sample of individuals with OCD; in the second, we tested the ensuing model in an independent sample. Our initial analyses were exploratory in nature. Nonetheless, based upon clinical and theoretical accounts and existing empirical findings we had the following hypotheses: a) higher scores on the checking and obsessions factor would predict the presence of obsessions related to fear of saying certain things, non-violent mental intrusions (i.e., sounds, images), and mental compulsions and compulsive measures to prevent harm and terrible consequences, and b) higher scores on the symmetry and ordering factor would predict obsessions related to need to know or remember details and fear of not saying just the right thing, and touching and tapping compulsions.

1. Method 1.1. Participants Participants were 488 individuals with OCD who had been evaluated and diagnosed at one of two Canadian clinics (the Anxiety Research and Treatment Centre at St. Joseph’s Healthcare, Hamilton, and the Anxiety Disorders Clinic of the Centre for Addiction & Mental Health

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Table 1 Age, sex, and symptom characteristics of participants with obsessive-compulsive disorder Variable

Clinic sample (n = 381)

Genetic study sample (n = 107)

Total for both samples (N = 488)

Mean agea Sex ratio (males/females) Mean Y-BOCS: Obsessions Mean Y-BOCS: Compulsions Mean Y-BOCS: Total Mean number of current specified symptoms

34.87  9.71 179/202; 47/53% 11.10  3.14 11.39  3.28 22.49  5.67 13.12  8.13

32.89  8.50 40/67; 38/62% 11.09  4.09 10.97  4.32 22.06  7.93 12.34  7.38

34.44  9.48 219/269; 45/55% 11.10  3.37 11.30  3.54 22.40  6.23 12.95  7.98

Note: Y-BOCS = Yale-Brown Obsessive Compulsive Scale, Severity Scale. 0 a Significant difference between samples, t (1,190.83) = 2.06, p < 0.05 (separate variance estimates).

[CAMH], Toronto). Of these, 381 were regular clinic patients at one of these sites,1 and 107 were probands participating in a family/genetic study of OCD at the CAMH. As the design of this study required two independent samples—the first large, and the second approximating an n of 100—these two groupings seemed the most sensible basis for dividing the full sample. Thus, the family/genetic study group served as an independent sample for the analyses performed in Part II of the current study. The demographic and clinical characteristics of the samples are summarized in Table 1. There were no exclusion criteria. Within the clinic sample, 87 (23%) of individuals were diagnosed according to DSM-III-R criteria and 294 (77%) were diagnosed according to DSM-IV criteria. All individuals in the family/genetic study sample were diagnosed according to DSM-IV criteria. Participants meeting DSM-III-R criteria were diagnosed by clinical interview with an experienced staff psychiatrist specializing in anxiety disorders. For those individuals meeting DSM-IV criteria, diagnoses were made using the Structured Clinical Interview for DSM-IV (SCID-IV: First, Spitzer, Gibbon, & Williams, 1996), conducted by trained and experienced raters, and were confirmed in a second interview by a staff psychiatrist. All participants consented to the use of assessment data for research purposes. Severity of obsessive-compulsive symptoms for all participants was ascertained with the 10item severity scale of the Y-BOCS. There were no significant differences in Y-BOCS severity ratings for either obsessions or compulsions between the two differently diagnosed clinic groups. As indicated in Table 1, the clinic sample had a significantly higher mean age than the family/ genetic study sample; the two samples were comparable in sex ratio and severity and number of current OCD symptoms. 1.2. Procedure Ratings of OCD symptoms were obtained using the clinician-rated symptom checklist of the Y-BOCS. The full checklist comprises 74 items, with each representing one discrete obsessive or 1

A subset of 203 of the clinic sample were participants in a previous factor analytic study of symptom structure in OCD (Summerfeldt et al., 1999).

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compulsive symptom. Only 64 of these are true specified items, the remaining 10 are open-ended (i.e., ‘‘other’’) items. All are organized by the authors into 15 rationally derived categories of obsessions and compulsions, including two ‘‘miscellaneous’’ categories, comprising symptoms not clearly belonging to one of the 13 other named groups. The data used for analyses in this study were the 44 specified items subsumed under the seven named obsession categories and six named obsessions categories, as well as 18 of the 20 specified items of the miscellaneous obsessions and compulsions categories. The two remaining specified miscellaneous items–‘‘trichotillomania’’ and ‘‘other self-damaging or self-mutilating behaviors’’–were omitted from our analyses, chiefly because they were too infrequently endorsed. However, there were also rational grounds for their exclusion: both items may tap symptoms of disorders other than OCD (Goodman et al., 1989). Following procedure and rationale described in detail elsewhere (Summerfeldt et al., 1999), open-ended items were excluded from analysis, and only ratings of current symptoms were included. The model of OCD symptom structure adopted in this study was the four-factor model developed by Leckman et al. (1997) and replicated by Summerfeldt et al. (1999). This comprises the following: obsessions and checking (aggressive, sexual, religious, and somatic obsessions, and checking compulsions, with 23 items), symmetry and ordering (symmetry obsessions and ordering/arranging, counting, and repeating compulsions, with six items), cleanliness and washing (contamination obsessions and cleaning compulsions, with 13 items), and hoarding (hoarding/saving obsessions and hoarding/collection compulsions, with two items). 1.3. Data analyses Data analysis was performed using Statistica 5.3 for Windows (StatSoft, 1999), and was conducted in two stages, with the respective goals of model development and model testing. In the first part of our study, employing data from the larger of our two samples, we sought to determine the relative contribution of each of the four symptom factors to the prediction of each of the miscellaneous items being examined. Logistic regression analysis was used, which allows prediction of a discrete outcome, such as presence or absence of symptom, from a set of variables. This technique is well suited to the analysis of clinical data such as ours as it makes no assumptions about distribution of, or linear relationships among, predictors, or equivalence of variance across outcome categories (Tabachnick & Fidell, 1996). For each of the 18 miscellaneous symptom items, a single direct logistic regression analysis was performed to assess prediction of presence or absence of symptom, on the basis of the four symptom factors. These analyses require calculation of scores for each of the four symptom factors, to be entered as predictors in each logistic regression. There is no standardized method for calculating factor scores for the Y-BOCS symptom checklist, and several options are available (see Grice, 2001). The composition of the symptom checklist (i.e., dichotomous items and unequal numbers of items per a priori category) poses challenges to this. One method assigns a single score (0 through 2) to each of the 13 categories based on endorsement of at least one item as either present, absent, or principal, then sums these into corresponding factor scores (see Calamari et al., 1999; Mataix-Cols, Rauch, Manzo, Jenike & Baer, 1999). This may be problematic as it a) presupposes the factorial equivalence of all items, which is not supported by item-level factor analyses (see Summerfeldt et al., 1999), b) reduces multi-item data into a single-item ordinal

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measure, contrary to recommended psychometric practice (Nunnally & Bernstein, 1994), and c) by forcing equivalence in category scores, may not accurately reflect the clinical reality. For example, an individual with five contamination obsessions present, but with two hoarding obsessions and compulsions currently principal would be considered equivalent on the contamination and cleaning factor to an individual with a single cleaning compulsion, as well as being classified as a ‘‘hoarder’’. Finally, though rendering categories equivalent, this coding strategywith its drawbacks-still does not address the fact that factors are composed of disparate numbers of categories. For the present study, as the 13 rationally derived categories that make up the four factors contain disparate numbers of specified items, and we wished to enhance the equivalency of the factors, we instead adopted the following procedure. For each category, weighted scores were calculated by dividing the sum of items actually endorsed by the total number of potentially endorsable specified items in that category. Weighted category scores were then summed into their corresponding factors. The predictors for each logistic regression consisted of the resulting scores for each of the four factors. The dependent variable for each analysis was of one of 18 specified miscellaneous items, coded according to whether the symptom was absent (0) or present (1). To adjust for multiple analyses a Bonferroni correction was employed, with threshold level of significance set at p  0.003. In the second part of our study, we sought to test the reliability of the associations between miscellaneous symptoms and the four factors obtained in our logistic regression analyses. For this purpose, a single confirmatory factor analysis was performed with data from our second OCD sample, using maximum likelihood estimation based on correlation matrices. This analytic approach is highly appropriate for this purpose, as it explicitly hypothesizes a structural model, then tests the fit of the model to observed data. Here, we hypothesized a four-factor model that expanded upon the original in that it incorporated miscellaneous items into the factors with which they were reliably associated (i.e., p  0.003) in our logistic regression analyses. The main objective of this analysis was to test whether this new model provided acceptable fit to symptom data from an independent sample. Due to the nonnormality of the data, sample size, and problems posed by high indicator-perfactor ratios and the dichotomous (i.e., present vs. absent) format of Y-BOCS symptom data (Ding, Velicer, & Harlow, 1995; Marsh, Hau, Balla, & Grayson, 1998; Williams & Holahan, 1994), we employed the structural equation modeling technique of parceling, or using sets of items rather than single items as indicators (Kishton & Widaman, 1994). With this technique, distributions more closely approach a normal distribution than when using the original items. In addition, it allows for a more stable estimation when sample size is small (Hoyle, 1995). Three randomly derived parcels of homogeneous items for the first three factors were constructed from the existing factor items plus relevant miscellaneous items. Since the fourth factor, hoarding, was comprised of only three single items, each item was considered an indicator. Following the recommendations of Anderson and Gerbing (1984); Bentler (1990); Cole (1987), and Marsh, Balla and MacDonald (1988), the following criteria were used to indicate the closeness of fit of the model to the data: the adjusted goodness of fit index (GFI)  0.85, the adjusted goodness of fit index (AGFI)  0.80, the root mean square standardized residual (RMSSR)  0.10, and the comparative fit index (CFI)  0.90.

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Table 2 Summary of logistic regressions predicting miscellaneous Y-BOCS symptoms from symptom factors (n = 381) Y-BOCS Factor

Miscellaneous item (Y-BOCS number) Obsessions Know/remember details (32) Fear saying certain things (33) Fear not saying just the right thing (34) Fear losing things (35) Intrusive images (36) Intrusive sounds (37) Bothered by sounds (38) Unlucky numbers (39) Colors with significance (40) Superstitious fears (41) Compulsions Mental rituals (64) Excessive list making (65) Need to tell, ask, or confess (66) Need to touch, tap, or rub (67) Rituals, blinking staring (68) Measures to prevent: harm to self; others; terrible consequences (69) Ritualized eating behaviors (70) Superstitious behaviors (71)

Obsessions & checking

Symmetry

Contamination & cleaning

Hoarding

% with

Odds ratio (95% CI)

Odds ratio (95% CI)

Odds ratio (95% CI)

Odds ratio (95% CI)

37

1.9y(1.4–2.8)

1.4y (1.2–1.8)

1.4 (0.8 –2.2)

1.3 (1.0–1.7)

10

3.3y (2.0–5.4)

1.2 (0.8–1.7)

1.4 (0.6–2.9)

1.4 (0.9–2.0)

32

2.5y (1.7–3.6)

1.5y (1.2–1.9)

1.1 (0.7–1.8)

1.2 (0.9–1.6)

22 8 16 10

1.7

(1.2–2.5) 2.2y (1.3–3.7) 2.8y (1.8–4.4) 2.2y (1.4–3.6)

1.5y (1.1–1.9) 1.6
(1.1–2.3) 1.3 (1.0–1.8) 1.4 (1.0–2.1)

1.5 (0.9–2.6) 1.1 (0.5–2.5) 0.8 (0.4–1.7) 2.6
(1.2–5.5)

1.3 (1.0–1.7) 1.0 (0.6–1.5) 1.5

(1.1–2.2) 1.2 (0.8–1.7)

18 8

2.3y (1.5–3.5) 2.3y (1.4–3.9)

2.4y (1.7–3.2) 1.1 (0.8–1.7)

1.5 (0.8–2.9) 2.0 (0.9–4.5)

0.8 (0.6–1.2) 1.0 (0.6–1.6)

11

2.2y (1.4–3.4)

1.4
(1.0–2.0)

0.8 (0.4–1.6)

1.2 (0.7–1.6)

33 19

2.7y (1.9–3.8) 1.0 (0.7–1.5)

1.1 (0.9–1.4) 1.6y (1.2–2.1)

0.6 (0.4–1.0) 1.5 (0.8–2.6)

0.9 (0.7–1.2) 1.6y (1.2–2.2)

37

3.3y (2.2–4.9)

1.2 (1.0–1.5)

1.8

(1.2–3.0)

1.0 (0.8–1.3)

15

2.1y (1.4–3.2)

2.0y (1.5–2.7)

0.7 (0.4–1.4)

1.1 (0.8–1.6)

7

2.1

(1.2–3.8)

2.4y (1.5–3.8)

1.3 (0.5–3.3)

1.2 (0.8–2.0)

12

2.7y (1.7–4.2)

0.8 (0.5–1.1)

1.3 (0.7–2.5)

0.9 (0.6–1.3)

7

2.0

(1.2–3.5)

1.5
(1.0–2.4)

1.9 (0.8–4.5)

1.0 (0.6–1.7)

8

1.6 (1.0–2.6)

1.4 (1.0–2.0)

1.0 (0.4–2.0)

1.0 (0.6–1.6)


p < 0.05;

p < 0.01; ypBonn < 0.003.

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2. Results 2.1. Part I: Logistic regression Table 2 shows odds ratios (OR) and 95% confidence intervals (CI) for each of the four predictors in relation to the 18 miscellaneous items. Regression coefficients (B) and Wald statistics are reported here for results meeting the adjusted significance value of p < 0.003. In total, 16 (89 %) of the miscellaneous items examined were reliably predicted by one or two of the four symptom factors, according to the Wald criterion. Eleven miscellaneous items were uniquely associated with one of two factors. The obsessions and checking factor alone predicted six miscellaneous obsession items: ‘‘fear of saying certain things’’ (B = 1.19, Wald = 21.97), ‘‘intrusive images’’ (B = 0.81, Wald = 9.87), ‘‘intrusive nonsense sounds/noises’’ (B = 1.05, Wald = 22.14), ‘‘bothered by sounds’’ (B = 0.80, Wald = 10.89), ‘‘colors with significance’’ (B = 0.84, Wald = 10.36), and ‘‘superstitious fears’’ (B = 0.77, Wald = 11.10). The obsessions and checking factor alone also predicted three miscellaneous compulsion items: ‘‘mental rituals other than checking/counting’’ (B = 0.99, Wald = 29.28), ‘‘need to tell, ask, or confess’’ (B = 1.19, Wald = 35.25), and ‘‘measures (not checking) to prevent harm to self, harm to others, or terrible consequences’’ (B = 0.98, Wald = 18.87). The symmetry and ordering factor alone reliably predicted the miscellaneous obsession item, ‘‘fear of losing things’’ (B = 0.40, Wald = 9.42), and the miscellaneous compulsion item ‘‘rituals involving blinking/staring’’ (B = 0.87, Wald = 14.02). Five miscellaneous items were reliably associated with two of the four factors. Both the obsessions and checking factor and the symmetry and ordering factor predicted the three miscellaneous obsession items ‘‘need to know/remember details’’ (B = 0.66, Wald = 13.54; B = 0.36, Wald = 10.47, respectively), ‘‘fear of not saying just the right thing’’ (B = 0.92, Wald = 23.58; B = 0.42, Wald = 12.24, respectively) and ‘‘lucky/unlucky numbers’’ (B = 0.84, Wald = 15.20; B = 0.86, Wald = 29.18, respectively), as well as the miscellaneous compulsion ‘‘need to touch, tap or rub’’ (B = 0.74, Wald = 11.55; B = 0.69, Wald = 19.74, respectively). The miscellaneous compulsion item ‘‘excessive listmaking’’ was reliably predicted by both the symmetry and ordering factor (B = 0.50, Wald = 12.99), and the hoarding factor (B = 0.49, Wald = 10.96).

2.2. Part II: Confirmatory factor analysis To assess the reliability of an expanded four-factor model that included the 16 miscellaneous obsession and compulsion items reliably predicted in the first part of our study, a confirmatory factor analysis (CFA) was conducted with our independent second sample. Miscellaneous items that were predicted in the logistic regression analyses by more than one factor were considered multiple indicators in the analysis (i.e., they were allowed to load on more than one symptom factor). Thus, 13 miscellaneous items were posited to be associated with the obsessions and checking factor, seven with the symmetry and ordering factor, and one with the hoarding factor. The parameter estimates were moderate to high, ranging from 0.586 to 0.874, and all indices of goodness of fit were well above acceptable levels. The GFI was 0.958, the AGFI was 0.932, the RMRRS was 0.084 and the CFI was .985. Thus, the expanded four-factor model,

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with the 16 miscellaneous items included, had good fit to the data observed in our independent sample.

3. Discussion To our knowledge, this study is the most comprehensive yet undertaken with the aim of investigating the associations among miscellaneous symptoms of OCD and empirically derived OCD symptom factors. We used rigorous methods chosen to withstand the statistical difficulties posed by naturally occurring symptom data. We first determined the association of each of 18 miscellaneous items with four symptom factors in a large sample of individuals with OCD, then tested the ensuing model of associations in a second independent sample. Eighty-nine percent of the miscellaneous symptoms examined were reliably associated with one or two of the four symptom factors, with obsessions and checking and symmetry and ordering factors emerging as foremost predictors. The resulting model of associations showed good fit with data from the independent sample. The findings were consistent with our hypotheses. Several unanticipated relationships were also observed, including the reliable association of several miscellaneous symptoms with more than one symptom dimension. All the associations found appear to be conceptually meaningful, and largely congruent with existing empirical accounts (e.g., Leckman et al., 1997). The greatest number of uniquely predicted miscellaneous symptoms were associated with the obsessions and checking dimension. Miscellaneous obsessions followed three themes, all suggestive of a tendency toward anxious apprehension and amplified threat estimation. The first theme, evident in the fear of saying certain things, may be the core of the obsessions and checking factor: concerns about the commission and implications of undesirable impulsive acts (Summerfeldt et al., 1999). The second theme was intrusive mental phenomena (e.g., non-violent images and sounds, being bothered by sounds). Unlike aggressive, sexual, or religious obsessions, the content of these is not objectively disturbing. Two opposing theories can be used to interpret this finding. It may be evidence of a general deficit in cognitive inhibition (Bannon, Gonsalvez, Croft, & Boyce, 2002; Enright & Beech, 1993), or it may support the premise of cognitive appraisal models, that any mental intrusion may develop into an obsession if it evokes distorted anxiety-provoking appraisals of its implications, including for one’s mental status (e.g., as evidence that one is going insane; see Rachman, 1997, 1998). A final obsessional theme was superstitiousness, evident in such symptoms as colors with significance and superstitious fears. Superstitiousness has been found to be uniquely linked with checking compulsions in patients (e.g., Frost et al., 1993) and impaired mental control (i.e., intrusions and worry) in a nonclinical sample (Sica, Novara, & Sanavio, 2002), and was in both cases interpreted as evidence of a broad underlying need to ward off uncontrollable feared outcomes. All three miscellaneous compulsions uniquely associated with the obsessions and checking dimension were congruent with functional models of compulsions as acts undertaken to reduce anxiety caused by obsessions (American Psychiatric Association, 2000; Rachman & Hodgson, 1980). Items included mental rituals, the need to tell, ask or confess, and measures (not checking) to prevent harm or terrible consequences. The first of these warrants particular note. The classification ‘‘pure obsessions’’ was originally disputed on the grounds that individuals with no

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apparent rituals often actually engage in a range of covert (i.e., cognitive) neutralizing activities functionally equivalent to overt compulsions (Freeston & Ladouceur, 1997; Salkovskis & Westbrook, 1989). Our findings suggest that although these symptoms are relatively neglected in the Y-BOCS checklist (Foa & Kozak, 1995; Taylor, 1995), some of the compulsions allocated to its miscellaneous section do take this form. Interestingly, this may account for the finding in some studies of a pure obsessions factor (Baer, 1994; Mataix-Cols, Rauch, Manzo, Jenike & Baer, 1999): this factor, the one least often replicated (e.g., Leckman et al., 1997; Summerfeldt et al., 1999), may be in part an artifact of the exclusion of miscellaneous items from analyses. Similarly, clinical accounts suggest that the need to tell, ask, or confess—often in the form of reassurance seeking—serves as a type of anxiety alleviating checking with others (Rachman & Shafran, 1998). Unexpectedly, five miscellaneous symptoms were found to be robustly associated with more than one factor. In all but one case, these involved the obsessions and checking and symmetry and ordering factors, and encompassed many of the symptoms found by Leckman et al. (1997), and hypothesized in the present study, to be uniquely associated with the latter. Miscellaneous items in this group included the obsessive need to know/remember details, fear of not saying just the right thing, and lucky/unlucky numbers, and a single compulsion: need to touch, tap or rub. The remaining miscellaneous compulsion, excessive listmaking, was unique in being associated with both the symmetry and ordering and hoarding factors. The obsessions and checking and symmetry and ordering factors have been found to be empirically distinct (Summerfeldt et al., 1999), so it is unlikely that shared symptom variance alone accounts for these results. In addition, the analyses used in the present study to detect these associations identify unique contributions made by predictor variables (i.e., symptom factors); shared variance is excluded from analysis. Thus, a more compelling interpretation is that overtly similar OCD symptoms may be associated with disparate underlying motivations and mechanisms. Miscellaneous obsessions in this list may reflect anxious apprehension and harm avoidance, in line with the predominant theme of the obsessions and checking dimension already discussed. For example, obsessions about not saying just the right thing may revolve around the fear of articulating something inappropriate, offensive, or potentially harmful. Clinically, we have encountered many patients who report such obsessions in combination with anxiety alleviating mental checking or replaying of conversations. In contrast, however, this same obsession may reflect the preoccupying sense that the content, wording, or sound of spoken language must conform to absolute, yet often inarticulable, subjective criteria (Summerfeldt, Antony & Swinson, 2002), or ‘‘standards of rightness’’ (Leckman et al., 1994/1995). Thus, symmetry and exactness concerns may extend to the spoken word. Similarly, obsessions related to lucky/unlucky numbers are congruent with the superstitiousness theme we observed in other obsessions and checking related miscellaneous items, but may also relate to counting compulsions, part of the symmetry and ordering factor. The possibility of disparate motivations underlying the same overt behavior is most striking with regard to the unanticipated finding that the need to touch, tap, or rub was strongly associated with both the obsessions and checking and symmetry and ordering factors. The objective similarity of touching and tapping compulsions to complex motor tics often makes the two difficult to distinguish (Cath et al., 2001; Miguel et al., 1995). Furthermore, these behaviors have been found to be most prevalent in individuals with OCD and comorbid tic-related disorders

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(e.g., Holzer et al., 1994; Leckman at al., 1994/1995), where they are often motivated by the need to correct a vague feeling of sensory discomfort or one’s being ‘‘not just right’’ (see Leckman, Walker, Goodman, Pauls, & Cohen, 1994; Miguel et al., 1995, 1997, 2000). As such, they show phenomenological overlap with symmetry and ordering symptoms. However, as Miguel et al. (1995) have noted, the same intentional repetitive behaviors may, like more complex compulsive rituals, arise from the need to neutralize intrusive thoughts. Our finding of the link between touching and tapping compulsions and the obsessions and checking factor supports this observation. Contrary to expectation, the symmetry and ordering dimension was uniquely associated with only two miscellaneous symptoms. Although the one compulsion, blinking and staring, has received little empirical attention, it is conventionally considered part of a tic-related constellation of OCD symptoms, like touching and tapping, and with similar associated subjective experiences (Miguel et al., 1995, 1997). Clinical accounts suggest that the one obsession, fear of losing things, may be an expression of the need for structure and regularity in one’s environment that characterizes symmetry and ordering symptoms (see Reed, 1985). The observed link between this dimension and listmaking could be similarly interpreted. The present study has limitations. Most notably, we adopted stringent statistical criteria to reduce the likelihood of Type I error in our exploratory analyses. As indicated in Table 2, an additional five symptoms, 28 percent of those analyzed, showed associations with symptom factors which, though not meeting our corrected significance criterion, were significant at p = 0.001. All but one of these were items accounted for by other symptom factors. Preliminary inspection suggests that at least some of these relationships may be meaningful. For example, compulsive rituals involving blinking or staring, associated with the symmetry and ordering factor, were also predicted, albeit below criterion, by the obsessions and checking factor. This connection may be amenable to the interpretation already offered for these factors’ joint prediction of touching and tapping compulsions, another tic-like behavior that may have more than one motivation (Miguel et al., 1995). In short, more inter-relationships among miscellaneous symptoms and factor dimensions may emerge in future research. An additional caveat about the findings of the present study relates to the analyses used. Logistic regression partitions unique from shared variance, and uses only the former in determining the relative strength of variables in the prediction of an outcome—in our case the presence or absence of a miscellaneous symptom. If shared variance among two or more predictor variables is responsible for an outcome, then only that predictor with the greatest unique contribution will emerge as significant. It is not unlikely that this at least partly accounts for the absence of any robust associations of miscellaneous symptoms with the contamination and cleaning factor. Studies using the Y-BOCS have found considerable empirical overlap between this and the obsessions and checking factor (Baer, 1994; Summerfeldt et al., 1999). Thus, our findings do not preclude the linkage between the contamination and cleaning factor and miscellaneous symptoms; they only suggest that if there is anything about this symptom domain that predicts miscellaneous items, it is likely accounted for by whatever characteristics it shares with the obsessions and checking factor. This methodological caveat serves to underscore a broader conceptual issue. As we have noted elsewhere with respect to other data (Summerfeldt et al., 1999), our findings provide grounds for reservation about the soundness of relying upon overt symptom similarities to

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identify a taxonomy of OCD. This practice overlooks the fact that overtly similar behaviors may have highly dissimilar underlying causes and functions, and the converse (see Miguel et al., 1995; Rasmussen & Eisen, 1988, 1992). The analyses employed in our study, like those behind all prevailing models of OCD symptom structure (Baer, 1994; Leckman et al., 1997; MataixCols, Rauch, Manzo, Jenike & Baer, 1999), simply identify the reliable co-occurrence of symptoms in the same individual. Models produced by such methods are solely descriptive, and are limited by the nature of the data submitted to analysis. With a few exceptions, the Y-BOCS checklist items analyzed in this and other factor analytic-based studies represent what the individual does, rather than why the individual does it. This not necessarily a failing of the Y-BOCS checklist per se, when used according to its original design as a purely descriptive, optimally reliable, catalogue of OCD symptoms. However, it may pose limitations when the measure is used as a taxonomic tool, as is becoming increasingly common. Our current finding of joint predictions of the same miscellaneous symptoms by different symptom factors, in combination with existing findings of highly variable symptom associations within factors as well as substantial empirical overlap between ostensibly disparate factors (i.e., obsessions and checking and contamination and cleaning; Summerfeldt et al., 1999), suggest that the many symptom expressions in OCD may have meaningful commonalities, that can emerge in, but are not the same as, aggregations of symptoms. Drawing upon the work of Rasmussen & Eisen, 1988, 1990, 1992) our group has been exploring the utility of a dimensional model of OCD which instead emphasizes the discrete motivational and affective features that underlie symptoms, and posits the existence of two core dimensions in OCD—Harm Avoidance and Incompleteness. The former, showing marked similarity to other anxiety disorders, is dominated by anxious apprehension and exaggerated avoidance of potential harm. The latter is unique to obsessive-compulsive phenomena, with the individual driven by a need to correct an inner dissatisfying sense of imperfection—a feeling of ‘‘not just right’’ (Leckman et al., 1994)— connected with the perception that actions or intentions have been incompletely achieved (Summerfeldt, 1998; Summerfeldt, Antony, & Swinson, 2002). Others have proposed classification based upon the different cognitive schemata that may underlie symptoms (Sookman, Pinard, & Beck, 2001). Such alternatives to symptom-based subtyping warrant investigation. The mounting factor-analytic evidence for the clustering of symptoms on purely empirical grounds prompts debatable questions about scale development or revision. On the one hand, revision or re-arrangement of the Y-BOCS to more closely reflect factor-analytic models could have advantages, such as permitting severity ratings to be made for each of the comprising symptom factors (see, for example, Leckman et al., 2000). This would address problems posed by the exclusively binary data provided by the current checklist, which do not truly permit accurate ascertainment of the relative dominance of symptom domains, either at baseline or subsequently (e.g., post-treatment). However, arguments could be made against such a revision at this time. Firstly, it would require standardized adoption of a single symptom structure model, when currently there is insufficient consensus to justify this. Second is the issue, already mentioned, of the questionable taxonomic value of groupings based solely upon overt behavioral similarities. Third, and more important, is a crucial weakness of all existing factor analytic models of OCD symptom structure based on the checklist. None were developed, or have been found to be reproducible, at the level of individual symptoms (see Summerfeldt et al., 1999).

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Thus, the literature on OCD symptom structure is on dubious foundations, and revision or development of other measures to reflect it may be premature. In summary, the current study has identified reliable associations among established symptom dimensions and a number of the less readily categorized but clinically well-recognized miscellaneous symptoms of OCD. Our findings provide justification for an expanded version of the four-factor model of OCD symptoms proposed by Leckman et al. (1997). It is worth noting, however, that this model is not the only one currently available (see Baer, 1994; Mataix-Cols, Rauch, Manzo, Jenike & Baer, 1999). Nor is it likely the most comprehensive model possible: it, like the others, is derived from category-level symptom data, and does not easily account for relationships among specific symptoms (Summerfeldt et al., 1999). Future research is needed to determine not only the replicability of our findings, but their compatibility with alternate models of symptom structure. Although the findings presented here are descriptive, they appear to be clinically and theoretically meaningful. As such, they may aid clinical understanding of the more unusual symptoms seen in OCD, and help to broaden the scope of research using symptom factors to guide investigation of the disorder’s causes and correlates.

Acknowledgements This research was supported in part by funding from the Ontario Mental Health Foundation (OMHF), in the form of a New Investigator Fellowship to Laura J. Summerfeldt and a Research Grant to Margaret A. Richter. The authors thank Meagan MacKenzie for her help preparing the manuscript.

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