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Reliability and validity of two Likert versions of the Schizotypal Personality Questionnaire (SPQ)
Personality and Individual Differences 38 (2005) 1543–1548 www.elsevier.com/locate/paid
Reliability and validity of two Likert versions of the Schizotypal Personality Questionnaire (SPQ) Viviana Wuthrich *, Timothy C. Bates Macquarie Centre for Cognitive Science, Macquarie University, Sydney, NSW 2109, Australia Received 27 January 2004; received in revised form 15 July 2004; accepted 23 September 2004 Available online 30 November 2004
Abstract Two alternative formats of the Schizotypal Personality Questionnaire (SPQ: Raine, 1991) were compared to examine if a Likert format in which SPQ items could be interleaved with other personality measures would promote reporting of symptoms. The Likert versions correlated highly with the standard SPQ (0.88–0.94) and showed better internal reliability compared to the standard version in which three subscales had Cronbach a < 0.70. The Likert versions also identified additional high scorers missed by the standard version and so may be desirable when testing relatives of patients with schizophrenia. Norms for the new version administered to 834 subjects are provided. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: SPQ; Schizotypy; Schizotypal Personality Disorder; Validity; Schizotypal Personality Questionnaire
1. Introduction The Schizotypal Personality Questionnaire (SPQ: Raine, 1991) is a 74 item self-report questionnaire measuring the nine diagnostic criteria of the DSM-III-R (American Psychiatric Association, 1987) Schizotypal Personality Disorder (SPD): odd speech, odd behaviour, unusual perceptual experiences, paranoia, no close friends, constricted affect, magical thinking, social anxiety, ideas *
Corresponding author. Fax: +61 2 9850 6059. E-mail address: [email protected] (V. Wuthrich).
0191-8869/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.paid.2004.09.017
1544
V. Wuthrich, T.C. Bates / Personality and Individual Differences 38 (2005) 1543–1548
of reference. A brief version of the scale SPQ-B is also available (Raine & Benishay, 1995). Since its publication, the SPQ has been widely used as a self-report tool for research into Schizotypal Personality Disorder (SPD) and also non-clinical levels of schizotypy or schizotypal features in the normal population. Mirroring other data on SPD, high scorers on the SPQ demonstrate deficits in language (Moritz et al., 1999), spatial working memory (Park & McTigue, 1997), executive functioning (Moritz, Andresen, Naber, Krausz, & Probsthein, 1999), and habituation to orienting stimuli (Raine, Benishay, Lencz, & Scarpa, 1997). Adequate reliability and validity have been met (see Raine, 1991), and therefore the SPQ appears to be a valid measure of SPD as defined by the DSM. The SPQ is administered in a forced choice format in which items indicative of SPD symptomatology are positively endorsed. We wanted to examine the validity of Likert versions of this scale to enable comparison of SPQ symptoms with normal personality traits measured in a Likert format and to disguise the unusualness of SPD symptoms by both allowing partial endorsement of items and by intermixing them with more normal and potentially more socially desirable personality traits to encourage disclosure. This is particularly important given that some researchers have suggested that relatives of patients with schizophrenia or SPD may be reluctant to disclose schizophrenia like symptoms and thus limiting research in this area (Jones et al., 2000; Peltier & Walsh, 1990). Therefore we administered three versions of the SPQ to university students (one original format and two Likert versions: one paper and one computerized) across two to three testing sessions.
2. Method 2.1. Participants Eight-hundred and thirty-four first year psychology students (212 male, 620 female and 2 unknown) participated for course credit (age range = 18–67, mean = 24.03, SD = 7.82). Not all participants completed all versions due to time constraints (see below).
3. Materials and scoring Three versions of the SPQ were administered. The forced choice version was the original 74 items of the SPQ (Raine, 1991) presented on paper with participants responding by circling either ‘‘yes’’ or ‘‘no’’ for each item. In conjunction with Raine (1991), this scale was scored with ‘‘yes’’ responses generating one point. A Likert version was also presented on paper in which participants circled either ‘‘strongly disagree’’, ‘‘disagree’’, ‘‘neutral’’, ‘‘agree’’, ‘‘strongly agree’’. This Likert version was presented again in a computerised form as part of a personality battery. The battery also contained the items from the Satisfaction with Life Scale (Diener, Emmons, Larsen, & Griffin, 1985), Machiavellian Scale (Christie & Geis, 1970), Psychopathy Scale (Levenson, Kiehl, & Fitzpatrick, 1995), Hypomania Scale (Eckblad & Chapman, 1986) and the Infrequency Scale (Chapman & Chapman, unpublished). Approximately every third item was an SPQ item. The participants responded by clicking the appropriate button on the screen using the five-point
V. Wuthrich, T.C. Bates / Personality and Individual Differences 38 (2005) 1543–1548
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Likert scale responses described above. The Likert versions were scored as follows: strongly disagree = 0, disagree = 1, neutral = 2, agree = 3, strongly agree = 4. Scores for all 74 items on each of the three versions were totaled to produce one score for each version. Scores for the nine subscales and three factors (interpersonal, cognitive/perceptual, disorganization) were calculated as described by Raine (1991). 3.1. Procedure All participants completed the computerised Likert version as part of other studies (Wuthrich & Bates, submitted for publication). Within 3 months a subset of students completed the SPQ forced choice (N = 60) and/or paper Likert versions (N = 67) as part of testing sessions on cognitive function, with one version completed at the beginning and one at the end of testing, with a random order of presentation.
4. Results The mean, standard deviation (SD), N, range of scores and 10% cutoff values for each version, along with the forced choice data from international samples are shown in Table 1. For the forced choice version, the means were very similar to those from Hall and Habbits (1996), although this Australian sample had a higher standard deviation. The mean for the computerised version was higher than the mean for the paper Likert version (127.09 vs 112.03: t(66) = 5.733, p < 0.001) but variances did not differ (44.42 vs 42.26: t(65) = 0.01 NS) by variance comparison test (Pitman, 1939; Zar, 1996). Disattentuated correlations of the three versions were as follows: SPQ forced choice and SPQ paper Likert r = 0.993 (n = 41); SPQ forced choice and SPQ computerised Likert r = 0.936 (n = 60); SPQ paper Likert and SPQ computerised Likert r = 0.919 (n = 67). These results suggest that either Likert version is a good substitute for the standard forced choice version. Coefficient as for the total score on each of the three versions were good: paper Likert (a = 0.96), computerised Likert (a = 0.95) and forced choice (a = 0.93). Subscale coefficients were good for the computer Likert version (0.77–0.90) and the paper Likert version (0.75–0.92). However, the coefficients for the forced choice version ranged from 0.58 to 0.90. Three subscales on this version failed to reach adequate levels of reliability (a < 0.70). These were constricted affect Table 1 Means, standard deviations and ranges Version
N
Mean
SD
90th percentile
Range of scores
Test range
Forced choice Paper Likert Computer Likert Raine (1991) (sample 2)a English sampleb
68 76 834 220 100
23.84 113.00 115.97 26.3 23.49
12.97 40.42 39.91 11.4 10.94
44.2 165.3 165 41 39
5–54 23–214 6–235 0–57 2–57
0–74 0–296 0–296 0–74 0–74
a b
Raine (1991). Hall and Habbits (1996).
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V. Wuthrich, T.C. Bates / Personality and Individual Differences 38 (2005) 1543–1548
Table 2 Internal reliability for the three versions of the SPQ Subscales
Computer Likert
Paper Likert
Forced choice
Raine (1991) (sample 2)
Social anxiety Constricted affect No close friends Paranoia Ideas of reference Magical thinking Unusual perceptual experiences Odd speech Odd behaviour Total score
0.85 0.77 0.80 0.84 0.82 0.83 0.81 0.83 0.90 0.95
0.89 0.75 0.83 0.90 0.83 0.86 0.85 0.88 0.92 0.96
0.86 0.58 0.68 0.74 0.78 0.85 0.69 0.80 0.90 0.93
0.68 0.65 0.74 0.73 0.71 0.75 0.73 0.63 0.74 0.91
NB: Italics indicate subscales with inadequate internal reliability (a < 0.70).
(0.58), unusual perceptual experiences (0.69), and no close friends (0.68). Constricted affect scored the lowest reliability coefficient across the three versions (see Table 2). Given that Raine (1991) reported that 55% of scorers in the top 10% are likely to meet criteria for SPD, we lastly examined whether the respondents identified in the top 10% on the standard version were also identified by the Likert versions. We used the forced choice version to identify the number of hits (correct identification), misses (missed identification), false alarms (incorrect classification) and correct rejections (correct rejections) that occurred for each of the Likert versions for the top 10% of the forced choice version (score P 44.2). See Table 3 for a summary of the results. For the paper Likert version, there were 4/4 hits, 0 misses, and 2 false alarms, and for the computer Table 3 Hits, misses, false alarms and correct rejections for the Likert versions Raw scores
Coding
Comments
Forced choice (N = 68)
Paper Likert (N = 76)
Computer Likert (N = 93)
Forced choice
Paper Likert
Computer Likert
38
165
204
0
1
1
187
0
163 187
0 0 0
215 210 177 209 200 225
1 1 1 1 1 1
40 41 43 44 46 48 48 53 53 54
157 152 183
189 194 166 214
1 0 0 1
1 1 1 1
0 1 1 1 0 1 1 1
False alarms or additional identifications False alarms or additional identification Correct rejection Correct rejection False alarm or additional identification Hit Hit Miss Hit Hit Hit
NB: Bold font identifies individuals scoring in the top 10% on the forced choice version (forced choice > 44.2). Coding = 1 represents if the individual scored in the top 10% of the sample on the specified version.
V. Wuthrich, T.C. Bates / Personality and Individual Differences 38 (2005) 1543–1548
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Likert version (N = 60), there were 5/6 hits, 1 miss and 3 false alarms. It is important to note that two people received false alarms by both the paper and computer Likert versions. Therefore these false alarms may actually represent a missed identification by the standard version. Having established the utility of the Likert SPQ, Table 1 may be used as a normative data base for future studies of student scores. This large (N = 834) sample indicates that schizotypy is negatively correlated with age (r = 0.262, p < 0.001) and that males score above females (120.79 vs 114.25, p < 0.05).
5. Discussion The results of this study indicate that the two Likert versions of the SPQ were at least as good as the standard SPQ version. This was indicated by the high correlations between the measures and the high percentage of hit rates within the top 10% of the sample across the three versions. In addition, the Likert versions were found to have better internal reliability, particularly at a subscale level. This is important given that in our sample, three of the subscales measures by the forced choice version failed to reach adequate levels of reliability (a < 0.70). While previous researchers (Jones et al., 2000; Peltier & Walsh, 1990), have cautioned that people may be reluctant to endorse schizotypy items on self-report questionnaires, this research suggests that most students are just as willing to endorse schizotypy items in the original (forced choice) format, as they are when items are intermingled with other more socially desirable personality characteristics and are less detectable as ‘‘unusual’’ items. However, in addition to correctly identifying hits, the Likert versions also identified several Ôfalse alarmsÕ. Given that both the Likert versions identified the same people as false alarms, these false alarms may instead reflect missed identifications by the forced choice version (false negatives). If this is true, then this suggests that a small portion of people may be more willing to disclose schizotypal symptoms using a Likert format than a forced choice format. Interestingly the computerized version was not superior to the paper Likert version even though SPQ items were hidden amongst other personality variables. One person scoring in the top 10% on the Forced Choice version scored below this rank on the computer Likert version. Overall, the data suggest that our Likert version of the SPQ may be better able to detect more guarded respondents, and therefore may be both more practical for many purposes as well as being more valid for the measurement of schizotypal symptoms amongst the relatives of patients with schizophrenia.
Acknowledgment Viviana Wuthrich conducted this research while a Fellow of the NSW Institute of Psychiatry.
References American Psychiatric Association. (1987). Diagnostic and statistical manual of mental disorders (3rd ed., revised). Washington, DC: American Psychiatric Association.
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V. Wuthrich, T.C. Bates / Personality and Individual Differences 38 (2005) 1543–1548
Chapman, L. J., & Chapman, J. P. Infrequency Scale (unpublished). Christie, R., & Geis, F. L. (1970). Studies in machiavellianism. New York: Academic Press. Diener, E., Emmons, R. A., Larsen, R. J., & Griffin, S. (1985). The satisfaction with life scale. Journal of Personality Assessment, 49, 71–75. Eckblad, M., & Chapman, L. J. (1986). Development and validation of a scale for hypomanic personality. Journal of Abnormal Psychology, 95, 214–222. Hall, G., & Habbits, P. (1996). Shadowing on the basis of contextual information in individuals with schizotypal personality. British Journal of Clinical Psychology, 35, 595–604. Jones, L., Cardno, A., Murphy, K., Sanders, R., Gray, M., McCarthy, G., et al. (2000). The Kings Schizotypy questionnaire as a quantitative measure of schizophrenia liability. Schizophrenia Research, 45(3), 213–221. Levenson, M. R., Kiehl, K. A., & Fitzpatrick, C. M. (1995). Assessing psychopathic attributes in a noninstitutionalised population. Journal of Personality and Social Psychology, 68, 151–158. Moritz, S., Andresen, B., Domin, F., Martin, T., Probsthein, E., Kretschmer, G., et al. (1999). Increased automatic spreading activation in healthy subjects with elevated scores in a scale assessing schizophrenic language disturbances. Psychological Medicine, 29(1), 161–170. Moritz, S., Andresen, B., Naber, D., Krausz, M., & Probsthein, E. (1999). Neuropsychological correlates of schizotypal disorganisation. Cognitive Neuropsychiatry, 4(4), 343–349. Park, S., & McTigue, K. (1997). Working memory and the syndromes of schizotypal personality. Schizophrenia Research, 26(2–3), 213–220. Peltier, B. D., & Walsh, J. A. (1990). An investigation of response bias in the Chapman scales. Educational and Psychological Measurement, 50, 803–815. Pitman, E. J. G. (1939). A note on normal correlation. Biometrika, 31, 9–12. Raine, A. (1991). The SPQ: A scale for the assessment of schizotypal personality based on DSM-III-R criteria. Schizophrenia Bulletin, 17(4), 555–564. Raine, A., & Benishay, D. (1995). The SPQ-B: A brief screening instrument for schizotypal personality disorder. Journal of Personality Disorders, 9(4), 346–355. Raine, A., Benishay, D., Lencz, T., & Scarpa, A. (1997). Abnormal orienting in schizotypal personality disorder. Schizophrenia Bulletin, 23(1), 75–82. Wuthrich, V., & Bates, T. C. (submitted for publication). Confirmatory factor analysis of the 3 factor structure of the schizotypal personality questionnaire and Chapman schizotypy scales. Zar, J. (1996). Biostatistical analysis (3rd ed.). New Jersey: Prentice Hall International Inc.
Reliability and validity of two Likert versions of the Schizotypal Personality Questionnaire (SPQ) Viviana Wuthrich *, Timothy C. Bates Macquarie Centre for Cognitive Science, Macquarie University, Sydney, NSW 2109, Australia Received 27 January 2004; received in revised form 15 July 2004; accepted 23 September 2004 Available online 30 November 2004
Abstract Two alternative formats of the Schizotypal Personality Questionnaire (SPQ: Raine, 1991) were compared to examine if a Likert format in which SPQ items could be interleaved with other personality measures would promote reporting of symptoms. The Likert versions correlated highly with the standard SPQ (0.88–0.94) and showed better internal reliability compared to the standard version in which three subscales had Cronbach a < 0.70. The Likert versions also identified additional high scorers missed by the standard version and so may be desirable when testing relatives of patients with schizophrenia. Norms for the new version administered to 834 subjects are provided. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: SPQ; Schizotypy; Schizotypal Personality Disorder; Validity; Schizotypal Personality Questionnaire
1. Introduction The Schizotypal Personality Questionnaire (SPQ: Raine, 1991) is a 74 item self-report questionnaire measuring the nine diagnostic criteria of the DSM-III-R (American Psychiatric Association, 1987) Schizotypal Personality Disorder (SPD): odd speech, odd behaviour, unusual perceptual experiences, paranoia, no close friends, constricted affect, magical thinking, social anxiety, ideas *
Corresponding author. Fax: +61 2 9850 6059. E-mail address: [email protected] (V. Wuthrich).
0191-8869/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.paid.2004.09.017
1544
V. Wuthrich, T.C. Bates / Personality and Individual Differences 38 (2005) 1543–1548
of reference. A brief version of the scale SPQ-B is also available (Raine & Benishay, 1995). Since its publication, the SPQ has been widely used as a self-report tool for research into Schizotypal Personality Disorder (SPD) and also non-clinical levels of schizotypy or schizotypal features in the normal population. Mirroring other data on SPD, high scorers on the SPQ demonstrate deficits in language (Moritz et al., 1999), spatial working memory (Park & McTigue, 1997), executive functioning (Moritz, Andresen, Naber, Krausz, & Probsthein, 1999), and habituation to orienting stimuli (Raine, Benishay, Lencz, & Scarpa, 1997). Adequate reliability and validity have been met (see Raine, 1991), and therefore the SPQ appears to be a valid measure of SPD as defined by the DSM. The SPQ is administered in a forced choice format in which items indicative of SPD symptomatology are positively endorsed. We wanted to examine the validity of Likert versions of this scale to enable comparison of SPQ symptoms with normal personality traits measured in a Likert format and to disguise the unusualness of SPD symptoms by both allowing partial endorsement of items and by intermixing them with more normal and potentially more socially desirable personality traits to encourage disclosure. This is particularly important given that some researchers have suggested that relatives of patients with schizophrenia or SPD may be reluctant to disclose schizophrenia like symptoms and thus limiting research in this area (Jones et al., 2000; Peltier & Walsh, 1990). Therefore we administered three versions of the SPQ to university students (one original format and two Likert versions: one paper and one computerized) across two to three testing sessions.
2. Method 2.1. Participants Eight-hundred and thirty-four first year psychology students (212 male, 620 female and 2 unknown) participated for course credit (age range = 18–67, mean = 24.03, SD = 7.82). Not all participants completed all versions due to time constraints (see below).
3. Materials and scoring Three versions of the SPQ were administered. The forced choice version was the original 74 items of the SPQ (Raine, 1991) presented on paper with participants responding by circling either ‘‘yes’’ or ‘‘no’’ for each item. In conjunction with Raine (1991), this scale was scored with ‘‘yes’’ responses generating one point. A Likert version was also presented on paper in which participants circled either ‘‘strongly disagree’’, ‘‘disagree’’, ‘‘neutral’’, ‘‘agree’’, ‘‘strongly agree’’. This Likert version was presented again in a computerised form as part of a personality battery. The battery also contained the items from the Satisfaction with Life Scale (Diener, Emmons, Larsen, & Griffin, 1985), Machiavellian Scale (Christie & Geis, 1970), Psychopathy Scale (Levenson, Kiehl, & Fitzpatrick, 1995), Hypomania Scale (Eckblad & Chapman, 1986) and the Infrequency Scale (Chapman & Chapman, unpublished). Approximately every third item was an SPQ item. The participants responded by clicking the appropriate button on the screen using the five-point
V. Wuthrich, T.C. Bates / Personality and Individual Differences 38 (2005) 1543–1548
1545
Likert scale responses described above. The Likert versions were scored as follows: strongly disagree = 0, disagree = 1, neutral = 2, agree = 3, strongly agree = 4. Scores for all 74 items on each of the three versions were totaled to produce one score for each version. Scores for the nine subscales and three factors (interpersonal, cognitive/perceptual, disorganization) were calculated as described by Raine (1991). 3.1. Procedure All participants completed the computerised Likert version as part of other studies (Wuthrich & Bates, submitted for publication). Within 3 months a subset of students completed the SPQ forced choice (N = 60) and/or paper Likert versions (N = 67) as part of testing sessions on cognitive function, with one version completed at the beginning and one at the end of testing, with a random order of presentation.
4. Results The mean, standard deviation (SD), N, range of scores and 10% cutoff values for each version, along with the forced choice data from international samples are shown in Table 1. For the forced choice version, the means were very similar to those from Hall and Habbits (1996), although this Australian sample had a higher standard deviation. The mean for the computerised version was higher than the mean for the paper Likert version (127.09 vs 112.03: t(66) = 5.733, p < 0.001) but variances did not differ (44.42 vs 42.26: t(65) = 0.01 NS) by variance comparison test (Pitman, 1939; Zar, 1996). Disattentuated correlations of the three versions were as follows: SPQ forced choice and SPQ paper Likert r = 0.993 (n = 41); SPQ forced choice and SPQ computerised Likert r = 0.936 (n = 60); SPQ paper Likert and SPQ computerised Likert r = 0.919 (n = 67). These results suggest that either Likert version is a good substitute for the standard forced choice version. Coefficient as for the total score on each of the three versions were good: paper Likert (a = 0.96), computerised Likert (a = 0.95) and forced choice (a = 0.93). Subscale coefficients were good for the computer Likert version (0.77–0.90) and the paper Likert version (0.75–0.92). However, the coefficients for the forced choice version ranged from 0.58 to 0.90. Three subscales on this version failed to reach adequate levels of reliability (a < 0.70). These were constricted affect Table 1 Means, standard deviations and ranges Version
N
Mean
SD
90th percentile
Range of scores
Test range
Forced choice Paper Likert Computer Likert Raine (1991) (sample 2)a English sampleb
68 76 834 220 100
23.84 113.00 115.97 26.3 23.49
12.97 40.42 39.91 11.4 10.94
44.2 165.3 165 41 39
5–54 23–214 6–235 0–57 2–57
0–74 0–296 0–296 0–74 0–74
a b
Raine (1991). Hall and Habbits (1996).
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V. Wuthrich, T.C. Bates / Personality and Individual Differences 38 (2005) 1543–1548
Table 2 Internal reliability for the three versions of the SPQ Subscales
Computer Likert
Paper Likert
Forced choice
Raine (1991) (sample 2)
Social anxiety Constricted affect No close friends Paranoia Ideas of reference Magical thinking Unusual perceptual experiences Odd speech Odd behaviour Total score
0.85 0.77 0.80 0.84 0.82 0.83 0.81 0.83 0.90 0.95
0.89 0.75 0.83 0.90 0.83 0.86 0.85 0.88 0.92 0.96
0.86 0.58 0.68 0.74 0.78 0.85 0.69 0.80 0.90 0.93
0.68 0.65 0.74 0.73 0.71 0.75 0.73 0.63 0.74 0.91
NB: Italics indicate subscales with inadequate internal reliability (a < 0.70).
(0.58), unusual perceptual experiences (0.69), and no close friends (0.68). Constricted affect scored the lowest reliability coefficient across the three versions (see Table 2). Given that Raine (1991) reported that 55% of scorers in the top 10% are likely to meet criteria for SPD, we lastly examined whether the respondents identified in the top 10% on the standard version were also identified by the Likert versions. We used the forced choice version to identify the number of hits (correct identification), misses (missed identification), false alarms (incorrect classification) and correct rejections (correct rejections) that occurred for each of the Likert versions for the top 10% of the forced choice version (score P 44.2). See Table 3 for a summary of the results. For the paper Likert version, there were 4/4 hits, 0 misses, and 2 false alarms, and for the computer Table 3 Hits, misses, false alarms and correct rejections for the Likert versions Raw scores
Coding
Comments
Forced choice (N = 68)
Paper Likert (N = 76)
Computer Likert (N = 93)
Forced choice
Paper Likert
Computer Likert
38
165
204
0
1
1
187
0
163 187
0 0 0
215 210 177 209 200 225
1 1 1 1 1 1
40 41 43 44 46 48 48 53 53 54
157 152 183
189 194 166 214
1 0 0 1
1 1 1 1
0 1 1 1 0 1 1 1
False alarms or additional identifications False alarms or additional identification Correct rejection Correct rejection False alarm or additional identification Hit Hit Miss Hit Hit Hit
NB: Bold font identifies individuals scoring in the top 10% on the forced choice version (forced choice > 44.2). Coding = 1 represents if the individual scored in the top 10% of the sample on the specified version.
V. Wuthrich, T.C. Bates / Personality and Individual Differences 38 (2005) 1543–1548
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Likert version (N = 60), there were 5/6 hits, 1 miss and 3 false alarms. It is important to note that two people received false alarms by both the paper and computer Likert versions. Therefore these false alarms may actually represent a missed identification by the standard version. Having established the utility of the Likert SPQ, Table 1 may be used as a normative data base for future studies of student scores. This large (N = 834) sample indicates that schizotypy is negatively correlated with age (r = 0.262, p < 0.001) and that males score above females (120.79 vs 114.25, p < 0.05).
5. Discussion The results of this study indicate that the two Likert versions of the SPQ were at least as good as the standard SPQ version. This was indicated by the high correlations between the measures and the high percentage of hit rates within the top 10% of the sample across the three versions. In addition, the Likert versions were found to have better internal reliability, particularly at a subscale level. This is important given that in our sample, three of the subscales measures by the forced choice version failed to reach adequate levels of reliability (a < 0.70). While previous researchers (Jones et al., 2000; Peltier & Walsh, 1990), have cautioned that people may be reluctant to endorse schizotypy items on self-report questionnaires, this research suggests that most students are just as willing to endorse schizotypy items in the original (forced choice) format, as they are when items are intermingled with other more socially desirable personality characteristics and are less detectable as ‘‘unusual’’ items. However, in addition to correctly identifying hits, the Likert versions also identified several Ôfalse alarmsÕ. Given that both the Likert versions identified the same people as false alarms, these false alarms may instead reflect missed identifications by the forced choice version (false negatives). If this is true, then this suggests that a small portion of people may be more willing to disclose schizotypal symptoms using a Likert format than a forced choice format. Interestingly the computerized version was not superior to the paper Likert version even though SPQ items were hidden amongst other personality variables. One person scoring in the top 10% on the Forced Choice version scored below this rank on the computer Likert version. Overall, the data suggest that our Likert version of the SPQ may be better able to detect more guarded respondents, and therefore may be both more practical for many purposes as well as being more valid for the measurement of schizotypal symptoms amongst the relatives of patients with schizophrenia.
Acknowledgment Viviana Wuthrich conducted this research while a Fellow of the NSW Institute of Psychiatry.
References American Psychiatric Association. (1987). Diagnostic and statistical manual of mental disorders (3rd ed., revised). Washington, DC: American Psychiatric Association.
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V. Wuthrich, T.C. Bates / Personality and Individual Differences 38 (2005) 1543–1548
Chapman, L. J., & Chapman, J. P. Infrequency Scale (unpublished). Christie, R., & Geis, F. L. (1970). Studies in machiavellianism. New York: Academic Press. Diener, E., Emmons, R. A., Larsen, R. J., & Griffin, S. (1985). The satisfaction with life scale. Journal of Personality Assessment, 49, 71–75. Eckblad, M., & Chapman, L. J. (1986). Development and validation of a scale for hypomanic personality. Journal of Abnormal Psychology, 95, 214–222. Hall, G., & Habbits, P. (1996). Shadowing on the basis of contextual information in individuals with schizotypal personality. British Journal of Clinical Psychology, 35, 595–604. Jones, L., Cardno, A., Murphy, K., Sanders, R., Gray, M., McCarthy, G., et al. (2000). The Kings Schizotypy questionnaire as a quantitative measure of schizophrenia liability. Schizophrenia Research, 45(3), 213–221. Levenson, M. R., Kiehl, K. A., & Fitzpatrick, C. M. (1995). Assessing psychopathic attributes in a noninstitutionalised population. Journal of Personality and Social Psychology, 68, 151–158. Moritz, S., Andresen, B., Domin, F., Martin, T., Probsthein, E., Kretschmer, G., et al. (1999). Increased automatic spreading activation in healthy subjects with elevated scores in a scale assessing schizophrenic language disturbances. Psychological Medicine, 29(1), 161–170. Moritz, S., Andresen, B., Naber, D., Krausz, M., & Probsthein, E. (1999). Neuropsychological correlates of schizotypal disorganisation. Cognitive Neuropsychiatry, 4(4), 343–349. Park, S., & McTigue, K. (1997). Working memory and the syndromes of schizotypal personality. Schizophrenia Research, 26(2–3), 213–220. Peltier, B. D., & Walsh, J. A. (1990). An investigation of response bias in the Chapman scales. Educational and Psychological Measurement, 50, 803–815. Pitman, E. J. G. (1939). A note on normal correlation. Biometrika, 31, 9–12. Raine, A. (1991). The SPQ: A scale for the assessment of schizotypal personality based on DSM-III-R criteria. Schizophrenia Bulletin, 17(4), 555–564. Raine, A., & Benishay, D. (1995). The SPQ-B: A brief screening instrument for schizotypal personality disorder. Journal of Personality Disorders, 9(4), 346–355. Raine, A., Benishay, D., Lencz, T., & Scarpa, A. (1997). Abnormal orienting in schizotypal personality disorder. Schizophrenia Bulletin, 23(1), 75–82. Wuthrich, V., & Bates, T. C. (submitted for publication). Confirmatory factor analysis of the 3 factor structure of the schizotypal personality questionnaire and Chapman schizotypy scales. Zar, J. (1996). Biostatistical analysis (3rd ed.). New Jersey: Prentice Hall International Inc.