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Psychometric properties of the Greek version of the Schizotypal Personality Questionnaire (SPQ) in young male obligatory conscripts: A two years test–retest study
Personality and Individual Differences 41 (2006) 1275–1286 www.elsevier.com/locate/paid
Psychometric properties of the Greek version of the Schizotypal Personality Questionnaire (SPQ) in young male obligatory conscripts: A two years test–retest study Nicholas C. Stefanis a,b,c,*, Silia Vitoratou a,d, Ioannis Ntzoufras d, Nikolaos Smyrnis a,b, Ioannis Evdokimidis a, Costas N. Stefanis a a
University Mental Health Research Institute (UMHRI) 2 Soranou tou Efessiou Str., P.O. Box 66517, 156 01 Papagou, Athens, Greece b Department of Psychiatry, National and Kapodistrian University of Athens, Greece Eginition Hospital, 74 Vas. Sofias Ave., 11528 Athens, Greece c King’s College London, Institute of Psychiatry, Department of Psychological Medicine, London, UK d Department of Statistics, University of Economics and Business, Patision 76, 104 34 Athens, Greece Available online 28 August 2006
Abstract The aim of this paper was the assessment of the psychometric properties of the Greek version of the Schizotypal Personality Questionnaire (SPQ), within the Athens Study of Psychosis Proneness and Incidence of Schizophrenia (ASPIS). The Greek version was administered to 1355 young male conscripts in the Greek Air Force. The Perceptual Aberration Scale (PAS) and Symptom Check List-90-Revised (SCL-90-R) were also included in the study in order to evaluate convergent and discriminant validity. Two years later the SPQ was re-administered to 145 of the conscripts followed by the Structured Interview for DSM-III-R Personality Disorders (SCID-II). The Greek SPQ version replicated the original author’s high internal reliability findings (0.91) providing evidence of convergent (0.70), discriminant (0.32–0.47) and criterion (0.81) validity. The stability estimator of the SPQ was found to be 0.53 while negative schizotypal features appeared to be more stable over time than positive ones. Thirty three percent of the individuals over the 90th percentile of the total SPQ score had a clinical diagnosis of Schizotypal Personality
*
Corresponding author. Address: Department of Psychiatry, National and Kapodistrian University of Athens, Greece Eginition Hospital, 74 Vas. Sofias Ave., 11528 Athens, Greece. Tel.: +30 6932 658067; fax: +30 210 7242020. E-mail address: [email protected] (N.C. Stefanis). 0191-8869/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.paid.2006.07.003
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Disorder (SPD) via the SCID-II interview, while none of the remaining individuals appeared to have this disorder. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Schizotypy; Validity; Reliability; SPD; SPQ; PAS; SCL-90-R; ASPIS
1. Introduction The study of the schizotypal personality traits in apparently normal individuals has received great attention due to genetic and epidemiological studies demonstrating that the schizotypal features cluster in subjects with elevated risk for schizophrenia and prodromal to the subsequent full manifestation of schizophrenia (review by Maier, Falkai, & Wagner, 1999). Two major theoretical approaches exist to explain the link between the schizotypal traits and schizophrenia. The theory of ‘‘schizotaxia’’ of Meehl (1962) proposes that schizotaxia is a conjectured neural integrative defect due to a dominant schizogene that gives rise to the schizotypal personality. This genetic profile implies vulnerability to schizophrenia and in synergy with other polygenic potentiators and adverse life experiences gives rise in a small percentage of these individuals to the clinical syndrome of schizophrenia. Another theoretical approach to schizotypal traits favoured by Eysenck (Eysenck & Eysenck, 1976) states that personality traits such as those that define psychoticism are a continuum from health to schizophrenia with no need to introduce arbitrary cut off points above which schizotypal traits lay as a different entity (Claridge, 1994). According to this view certain dimensions of personality can be found in the general population and their extremes lead to the symptoms of a disease state such as schizophrenia (van Os, Hanssen, Bijl, & Ravelli, 2000). Self-administered questionnaires have been used extensively in several studies examining the schizotypal personality traits. A self-administered questionnaire that assesses all nine aspects of the SPD according to the Diagnostic and Statistical Manual of Mental Disorders Revised DSM-III-R (American Psychiatric Association, 1987) is the Schizotypal Personality Questionnaire (SPQ) developed by Raine (1991). It can be used as a screening instrument in the general population for the identification of individuals with broad schizotypal traits (according to the author, 55% of top SPQ scorers obtained an interview-based SPD diagnosis), and may serve as a measure of individual differences in the schizotypal personality. As part of the ASPIS, the aim of the current study was to assess the psychometric properties of the Greek version of the SPQ in a large unselected sample of apparently healthy young males who are on the one hand at an age of heightened risk for schizophrenia and on the other experiencing a stressful change in life circumstances (Stefanis et al., 2004). 2. Methods 2.1. Participants The translated inventories SCL-90-R (Derogatis, 1993), SPQ and PAS (Chapman, Chapman, & Raulin, 1978) were administered (in this order) to 2243 randomly selected young male conscripts
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aged 18–24 years who were recruited from the Greek Air Force, during their first two weeks of admission in the National Basic Air Force training centre in the city of Tripoli. A team of military medical doctors of all specialties had already evaluated the conscripts as having a satisfactory medical condition, which allowed them to begin their obligatory service. All conscripts signed written consents after agreeing to participate in an anonymous survey. The degree of collaboration was evaluated using the four validity items of the Temperament and Character Inventory (TCI: Cloninger, Przybeck, Svrakic, & Wetzel, 1994). Using this instrument, 832 individuals (37.1%) were traced with disagreement in at least one of the four items (random responders). Scores of the subscales and overall each questionnaire were calculated only for those cases where at least 90% of the items were responded to. Total and subscale SPQ, PAS and SCL-90-R scores are therefore available for 1355, 1354 and 1344 individuals, respectively. After two years, a subsample of the individuals was summoned to participate in a retest analysis at the General Hospital of the Hellenic Air Force (GHHAF).The retest sample constituted of 209 individuals and was reduced to 145 after excluding random responders (23.4%) and individuals with more than the acceptable percentage of missing values (9.4%). For further research purposes the retest sample consisted mainly of individuals who had either scored over the 80th percentile of the total SPQ score in the first assessment (36%) or close to the mean value (40%). 2.2. Instruments The SPQ and PAS were translated into Greek and back translated into English by an independent official translator. Comparison of the original and the first English draft produced a second modified Greek version that received minor further changes. The second back translation was approved by the original questionnaire authors (Raine, A. & Kwapil, T. personal communication, January 1999). A Greek version and standardization of the SCL-90-R in the Greek population can be found in Donias, Karastergiou, and Manos (1991), while reliability analysis is provided in the current paper along with the SPQ and PAS. Furthermore, in order to explore AXIS II psychopathology, re-attenders at the GHHAF were assessed with the Structured Clinical Interview for DSM-III-R personality disorders (SCID-II) (Spitzer, Williams, & Gibbon, 1987) by trained interviewers blind to the self-rated schizotypal status of the conscripts. All data analysis was conducted on the SPSS 10.0 (1999) and STATA 6.0 (1999) statistical packages. 2.3. Analysis 2.3.1. Convergent, discriminant and criterion validity SCL-90-R is a 90-item self-report inventory consisting of nine subscales and three indices of psychological distress. Each subscale assesses symptoms of current psychopathology that do not overlap the SPD symptoms. Hence discriminant validity can be evaluated via the correlation between each SCL-90-R subscale and the SPQ total score. On the contrary, the PAS is a 35-item instrument which taps the perceptual aberration feature of the SPD similarly to the ‘‘Unusual Perceptual Experiences’’ subscale of the SPQ. Hence it can be used to assess convergent validity. Four PAS items (items 6, 13, 24 and 25) were excluded from the analysis due to translation discrepancies that could produce low face validity of the instrument.
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Among the 145 individuals participating in the second assessment of the SPQ at GHHAF, sixteen individuals did not volunteer to participate to the interview process and therefore 129 of the reliable responders on the SPQ finally were evaluated via the SCID-II. The SCID-II assesses all nine traits of the SPD while five have to be present for a positive diagnosis. The 3-point scale (1 indicates that the trait is not present, 2 indicates subthreshold and 3 threshold rating) was used for trait scoring while summing each trait’s score leads to a total SCID-II scoring.
3. Results 3.1. Descriptive indices and internal reliability Descriptive indices and alpha coefficients for the subscales and total SPQ are presented in Table 1 for the first assessment sample (along with the corresponding indices for the random responders whose missing values were not exceeded by 20% of the SPQ items: 420 individuals). The lower and upper cut off scores (ten-tiles) of the total SPQ scores were found equal to 12 and 44, respectively. Cronbach’s alpha coefficient was high (0.91) for the total score and satisfactory for the subscales (0.58–0.80). Seven problematic items were traced (6, 28, 33, 37, 49, 62 and 65) with low item-total correlations (lower than 0.20) and no decrease of alpha at item deletion. However, only item 49 was problematic within its corresponding scale. The SPQ scores were found to correlate negatively with age (r = 0.18, p < 0.001). The internal consistency of the PAS was also found to be satisfactory with alpha being equal to 0.88. The mean PAS score was 5.17 (n = 1354, median = 4.00, SD = 5.24) while the values ranged from 0 to 30. The distribution of PAS scores was skewed (1.55) and the lower and upper cut off ten tiles were equal to zero and twelve, respectively. No problematic items were traced since the item total correlations were ranged from 0.28 to 0.50.
Table 1 Descriptive indices and alpha coefficients for subscales and total SPQ, first assessment sample (n = 1355)a SPQ subscale
Alpha
Ideas of reference Social Anxiety Odd Beliefs/Magical Thinking Unusual Perceptual Experiences Odd Behaviour and Appearance No Close Friends Odd Speech Constricted Affect Suspiciousness/Paranoid Ideation
0.66 0.76 0.58 0.72 0.80 0.58 0.73 0.63 0.69
Total Score
0.91 (0.90)
*
(0.57) (0.67) (0.57) (0.68) (0.65) (0.61) (0.57) (0.60) (0.61)
Mean *
SD
Range
4.98 (4.61) 3.20* (3.49) 1.98* (2.45) 2.61* (3.30) 2.75* (3.05) 2.29* (3.26) 3.85 (3.97) 2.12* (2.97) 3.75 (3.93)
2.10 2.30 1.62 2.17 2.24 1.80 2.41 1.80 2.06
(2.01) (2.19) (1.75) (2.24) (1.95) (2.06) (2.09) (1.93) (1.97)
27.78* (31.09)
12.35 (12.34)
0–9 0–8 0–7 0–9 0–7 0–9 0–9 0–8 0–8 0–68
The scores between reliable and random responders were statistically different according t-test (p < 0.05). Within parentheses are presented the corresponding descriptive indices for the random responders with less than 50% missing values (n = 410). a
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The overall subscale alpha coefficient was also high (0.97) in the case of the SCL-90-R, while the corresponding coefficients for each subscale were found to range from 0.66 to 0.87. The item total correlations ranged from 0.28 to 0.60, so no problematic items were traced. 3.2. Test–retest reliability The stability of the total SPQ score was moderate with the Pearson correlation being equal to 0.53 (p < 0.001). The lowest test–retest coefficients were calculated for the subscales that assess the positive features of the SPD and the highest for the subscales that assess those that are negative. There were no significant differences (z-based Pearson-Filon: ZPF, Dunn & Clark, 1969) within the coefficients of the subscales for the positive features while they were significantly lower than the coefficients for those that are negative with the exception in the ‘‘No close friends’’ subscale (Table 2). Furthermore, a severe decrease in the subscale (34.8–68.4%) and total SPQ (48.1%) scores was present. The differences in the decreases were tested (adjusting subscale scores for the number of items included) but no particular pattern became apparent since the statistically significant differences were randomly distributed among the subscales. 3.3. Convergent and discriminant validity The correlation between the PAS and the SPQ subscale of ‘‘Unusual Perceptual Experiences’’ was found to be satisfactory (0.70), while the correlations between the PAS and the rest of the SPQ subscales were much lower ranging from 0.32 to 0.45 (Table 3). The correlation between the total SPQ score and each of the nine subscales of the SCL-90-R ranged from 0.35 to 0.47. Furthermore, the correlations between both SPQ and SCL-90-R subscales were found to be lower than 0.45 (p < 0.001, in all cases). Each coefficient between the PAS score and SPQ subscales and between the subscales of the SPQ and the SCL-90-R was significantly lower than the
Table 2 Test–retest reliability and mean difference on SPQ scores, between assessment samples (n = 145) SPQ subscalea
Test–retest coefficient*,b N2,N3,D1,D2
P1. Unusual Perceptual Experiences P2. Ideas of reference P3. Odd Beliefs/Magical Thinking PN. Suspiciousness/Paranoid Ideation N1. No Close Friends D1. Odd Behaviour and Appearance D2. Odd Speech N2. Constricted Affect N3. Social Anxiety
0.29 0.32N2,N3,D2 0.35N2,N3,D2 0.37N2,N3,D2 0.41N3,D2 0.45N2,N3,P1 0.51P1,P2,P3,PN 0.58P1,P2,P3,PN,N1,D1 0.62P1,P2,P3,PN,N1,D1
Total Score
0.53
*
Mean score difference*
%
2.23 3.26 1.21 1.85 1.14 1.80 2.07 0.98 1.81
68.4 56.4 51.6 40.2 40.7 51.2 42.2 34.8 44.6
16.48
48.1
p < 0.001. P: positive, N: negative, D: disorganized feature. b The superscripts notify the id of the subscales with significantly different (p < 0.05) test–retest coefficients according ZPF. a
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Table 3 Correlations of SPQ subscales and total scores with convergent/discriminant validity subscales (first assessment sample, n = 1355) SCL-90-R subscale
SPQ total score* r
SPQ subscale
PAS score* r
Anxiety Depression Phobic Anxiety Hostility Interpersonal Sensitivity Obsessive-Compulsive Paranoid Ideation Psychoticism Somatization
0.47 0.47 0.42 0.35 0.42 0.46 0.39 0.42 0.37
Ideas of reference Social Anxiety Odd Beliefs/Magical Thinking Unusual Perceptual Experiences Odd Behaviour and Appearance No Close Friends Odd Speech Constricted Affect Suspiciousness/Paranoid Ideation
0.40 0.32 0.43 0.70 0.43 0.38 0.45 0.43 0.38
*
All correlation coefficients were statistically significant (p < 0.0001).
correlation between the PAS and the ‘‘Unusual Perceptual Experiences’’ subscale (Olkin, 1967, z for comparing dependent correlation coefficients, p < 0.001 in all cases). 3.4. Criterion validity From the total of the 129 valid retest cases interviewed with the SCID-II, 9 and 13 individuals were identified as high and low (respectively) SPQ scorers. Among the 9 individuals with a high SPQ score, three (33.3%) received a clinical diagnosis of the SPD while none of the remaining 120 individuals received such a diagnosis. This subsample that consists of the 22 high and low scorers was studied following Raine’s (1991) initial study. The clinical diagnosis of the SPD (positive/negative) was found to have positive but moderate associations with both group membership (high/ low; phi = 0.48, p = 0.025) and the SPQ total scores (point bi-serial r = 0.51 p = 0.016). The Spearman correlations between both SPQ scores and SCID-II ratings (Table 4) were moderate to high (0.38–0.90). For six of the subscales, the correlations were statistically significant while the other two were marginally significant (p < 0.10). In the case of ‘‘Odd Behaviour and Appearance’’ the SCID-II score was zero for all individuals and no correlation could be calculated. Total SPQ score was highly correlated with the SCID over-all-traits score (rSpearman = 0.81, p < 0.001). Furthermore, t-tests for two independent samples indicated that the mean score of the SPQ subscales were significantly higher (p < 0.05) when the trait was present, with the exception of the ‘‘Odd Speech’’ subscale where the mean difference was evidential of a trend (p = 0.114), even though the mean was higher in the trait present group. Among the 6 high scorers that did not receive a clinical diagnosis on the SPD, one individual did not show any SPD symptoms, while 4 others were rated with one or two subthresholds plus at least two threshold ratings. One further individual reached the threshold of the diagnosis by having four traits. The 120 individuals that did not meet the higher cut off score had significantly lower SCID-II over-all-traits scores (mean difference = 4.83, SD = 1.32, p < 0.0001). Apart from the retest subsample of the high and low scorers, the entire sample of the 129 individuals was also considered in this study. Using logistic regression, the odds ratio (OR) of receiv-
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Table 4 Correlations between SPQ scores and SCID-II ratings for each trait and total (second assessment subsample of high/ low scorers, n = 22) SPQ subscale
SCID-II interview r
1. 2. 3. 4. 5. 6. 7. 8. 9.
0.79* 0.90* 0.56* 0.40** – 0.52* 0.38** 0.65* 0.65*
Ideas of reference Social Anxiety Odd Beliefs/Magical Thinking Unusual Perceptual Experiences Odd Behaviour and Appearance No Close Friends Odd Speech Constricted Affect Suspiciousness/Paranoid Ideation
0.81*
Total Score * **
p < 0.05. p < 0.10.
ing a clinical diagnosis on the SPD via the SPQ score increment was calculated to be 1.27 (p = 0.011). Applying ordinal logistic regression (Table 5) at the 3-point rating of the SCID-II for each trait by score increment in the SPQ subscales, the ORs varied from 1.56 to 2.55. In the case of the ‘‘Odd Speech’’ the estimated OR was not significant (p = 0.450). The proportional-odds assumption was not violated in any model. 3.5. Factor structure The analysis of the factorial structure of the SPQ as defined by the responses of the 1355 conscripts can be found in Stefanis et al. (2004). Confirmatory factor analysis indicated that the three factor model (Cognitive/Perceptual, Disorganized and Interpersonal factor) suggested by Raine
Table 5 Odds ratios of receiving a SPD diagnosis by score increment in the SPQ subscales and total scores (second assessment sample, n = 129) SPQ subscale 1. 2. 3. 4. 5. 6. 7. 8. 9. * **
Ideas of reference Social Anxiety Odd Beliefs/Magical Thinking Unusual Perceptual Experiences Odd Behaviour and Appearance No Close Friends Odd Speech Constricted Affect Suspiciousness/Paranoid Ideation p < 0.001. p = 0.448.
OR
SE *
1.83 2.55* 1.97* 1.80* – 2.02* 1.10** 2.00* 1.56*
0.23 0.45 0.37 0.32 – 0.39 0.14 0.38 0.20
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Ideas of Reference
Cognitive Perceptual
Odd Beliefs Perceptual Experiences
Paranoid Suspiciousness Social Anxiety Negative No Close Friends Constricted Affect Disorganization Odd Behaviour Odd Speech
Fig. 1. Path representation of the proposed four-factor model (Stefanis et al., 2004). Table 6 Descriptive indices and alpha coefficients for the three factors model (first assessment sample, n = 1355) SPQ Factor
Alpha
Mean
SD
Range
1. Interpersonal 2. Cognitive-Perceptual 3. Disorganized
0.83 0.83 0.85
11.48 13.43 6.60
6.01 5.99 4.08
0–32 0–33 0–16
et al. (1994) provided a good fit to the data. However, better fit to the data was provided by a four factor model where positive schizotypy is further divided into a paranoid and a cognitive-perceptual factor (Fig. 1). The descriptive indices and alpha coefficients of the three sum-factors (summing the raw scores of the respective subscales) suggested by Raine et al. (1994), are given in Table 6.
4. Discussion The primary aim of this study was to assess the reliability and validity of the Greek version of the SPQ. Further, the psychometric indices of the PAS and SCL-90-R scales were estimated concurrently. In the first assessment sample three of the SPQ subscales had moderate alpha coefficients (0.58–0.63) and noticeably lower than the corresponding ones in Raine’s samples (Table 1). Furthermore, the item 49 (writing letters to friends is more trouble than it is worth) had low item-scale correlation with ‘‘no close friends’’. However the restricted age range of our sample may explain this, since more direct types of communication (such as mobile phone calls) are preferred by individuals of this age.
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As Raine, Venables, Mednick, and Mellingen (2002, p. 77), point out it is possible that ‘‘while some individuals are persistently schizotypal over time, some others change their status’’, even though it is commonly believed that schizotypal personality features remain stable throughout life. Indeed the stability of the SPQ subscales scores was found in this study to be low to moderate (0.29–0.62) for a time period of two years. It is possible then that several high scorers on schizotypal tests are ‘‘pseudo-schizotypals’’ receiving low scores in later studies. These values are comparable with the two years test–retest reliability estimators reported for the PAS and the Magical Ideation Scale (Eckblad & Chapman, 1983) by Meyer and Hautzinger (1999). As can be seen in Table 2, the lowest test–retest coefficients appear in the positive schizotypy dimension (0.29–0.35), the subscales referring to the ‘‘Disorganized factor’’ lie in between, while the negative features appear to be less affected during the 2 year time interval period (0.41–0.62). Negative schizotypy as a construct appears to be more stable over time than positive, adding to the accumulating evidence that schizotypal dimensions are influenced by somewhat different underlying genetic, pathophysiological and environmental processes (Siever, 1995; Stefanis et al., 2004). The subscale and total norms of the SPQ for the first assessment sample are similar to the corresponding ones of the American population as provided by Raine (1991), with analogous high and low cut off points. However, in the second assessment results a severe decrease in scores was present (34.8–68.4%). This generalized reduction in SPQ subscales at the retest time point (end of military training) can be attributed to the absence of environmental stressful circumstances that existed during the first assessment (stress associated with initiation of compulsory military service) and indicates that psychometrically defined schizotypal personality traits may be much more sensitive to environmental stressors than previously thought of. Finally, since age correlates negatively with the SPD features, the long time elapsed additionally justifies the lower scores. The SPQ demonstrated low correlations with the subscales that do not measure schizotypal features and high ones with the PAS evidencing discriminant and convergent validity, respectively. A high correlation between the PAS and the SPQ subscale of the ‘‘Unusual Perceptual Experiences’’ was found (0.70). Furthermore, the correlations between the PAS and the rest of the SPQ subscales were significantly lower and moderate in magnitude, ranging from 0.32 s0 0.45, indicating discriminant validity. Moreover, these results can be considered as confirmative of the PAS validity. This fact, in addition with the high internal consistency of the scale, demonstrates the good psychometric properties of the PAS Greek version (not including however items 6, 13, 24 and 25). Evidence in favour of the discriminant validity of SPQ were also provided by the correlations between the SPQ total and subscales scores and each of the nine subscales of the SCL-90-R ranging from low to moderate (0.35–0.47). All correlations between the SPQ and the discriminant subscales were significantly lower than the correlation used for convergent validity assessment. These validity estimators are comparable with the analogous ones in the American population provided by Raine (1991). During the second application of the SPQ in GHHAF, 129 of the 145 individuals also participated to a clinical evaluation via a SCID-II interview in order to assess criterion validity. Three individuals were found to meet the DSM-III-R criteria for the SPD. All three individuals had scored above the high cut-off score in the distribution of the SPQ total score at both time points. This yields an estimation of 33.3% of the high scorers expected to have this disorder. Since 5 high scorers of the initial retest sample of the 145 individuals were not interviewed, this percentage is
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only suggestive of the positive predictive value of the high cut off score criterion. Moreover, the individuals in the upper SPQ ten-tile with no SPD diagnosis, were found to have a substantial number of subthreshold or threshold ratings via the SCID-II interview. These results confirm that high SPQ scores are suggestive of SPD. The subsample that consists of the 22 high and low scorers yielded moderate to high positive correlations between each SPQ subscale score and the corresponding SCID-II rating, while the SPQ subscale scores were significantly higher for individuals with subthreshold or threshold ratings versus individuals that didn’t receive such a diagnosis for a specific trait. In addition, total SPQ scores were highly correlated with the SCID over-all-traits score (0.81) confirming that high SPQ scores evince individuals with at least a substantial number of subthreshold or threshold ratings. This is further indicated by the fact that the high scorer’s group had significantly higher SCID over-all-traits scores than the low scorers’ group. The positive association between the SPQ score and SPD symptoms is therefore confirmed by the current study, replicating Raine’s findings. The differences in the odds of receiving a SPD diagnosis by the increment of the SPQ scores were calculated for the entire second assessment subsample of the 129 individuals who concurrently assessed the SPQ and received a clinical evaluation via the SCID-II. The OR of receiving a SPD diagnosis (1.27) indicates that for each increment of the total SPQ score by positive item response, the odds to receive a SPD diagnosis increase by 27%. The difference in the odds of receiving a subthreshold or threshold rating of a particular trait by the SPQ score increment is even steeper. Under the proportional odds assumption it is hypothesized that a latent continuum lies beneath the three points SCID-II rating and regardless of the dichotomization of this rating for a particular trait, the OR is constant. Hence, the percent increment in the odds of receiving at least a subthreshold rating for a particular trait by positive item response on the corresponding subscale equals the expected increment in the odds of receiving at most subthreshold ratings (versus receiving threshold rating) and varies from 56% to 155% (Table 5). These estimations confirm that higher SPQ scores are robustly suggestive either of SPD or at least of the presence of particular traits at subscale level. Furthermore, confirming Raine’s (1991) hypothesis, none of the individuals beyond the high scorers’ group received a positive diagnosis. This indicates that the use of the 10% high cut-off score can be considered as a sensitive criterion in tracing individuals in normative populations with a potential SPD diagnosis.
5. Methodological limitations Our sample consisted of young males that were recruited in the military service. Thus it cannot be claimed that our findings could be directly generalized to the Greek population (men and women of every age). Both age and gender are consistently reported to modify the SPD measurements. In particular, age is reported to be negatively correlated with the SPQ scores while males score significantly higher on negative symptom subscales than females and significantly lower on positive ones (Raine, 1992). However, this sample can be considered representative of males in this age, since military service is obligatory in Greece. The high percentage of random responders in the study is attributed possibly to gains related to avoidance of military drills during the day of examination and subsequent indifference during
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testing procedures, and not due to genuine psychometrically deviant performance. Such an explanation is plausible since, even though the random responders had significantly augmented schizotypal scores compared to correct responders (Table 2), they exhibited significantly higher avoidance and escape patterns (SCL-90-R Phobic anxiety: mean difference = 0.12, p = 0.001) while not differing from correct responders in other SCL-90-R state psychopathology such as paranoid ideation, psychoticism, or depression (p > 0.05). The second assessment sample consisted mainly of high and moderate scorers of the first assessment sample. This might introduce some bias, even though all categories of scorers were represented (at least 3 individuals from each ten-tile of the first assessment). Moreover no analysis was performed to assess the degree of agreement between the interviewers of the SCID-II. Further information concerning the high percentage of random responders can be found in Stefanis et al. (2004).
References American Psychiatric Association (1987). DSM-III R: Diagnostic and statistical manual of mental disorders (3rd ed. revised). Washington, DC: APA. Chapman, L. J., Chapman, J. P., & Raulin, M. L. (1978). Body—image aberration in schizophrenia. Journal of Abnormal Psychology, 87, 399–407. Claridge, G. S. (1994). Single indicator of risk for schizophrenia: probable fact or likely myth? Schizophrenia Bulletin, 20, 151–168. Cloninger, C. R., Przybeck, T., Svrakic, D., & Wetzel, R. (1994). The Temperament and Character Inventory (TCI): A guide to its development and use. St. Louis, Missouri: Washington University, Centre for Psychobiology of Personality. Derogatis, L. R. (1993). Symptom Checklist-90-R (SCL-90-R). Minneapolis, MN: Computer Systems, Inc. Donias, S., Karastergiou, A., & Manos, N. (1991). Standardization of the symptom check-list-90-R rating scale in a Greek population. Psychiatriki, 2, 42–48. Dunn, O. J., & Clark, V. A. (1969). Correlation coefficients measured on the same individuals. Journal of the American Statistical Association, 64, 366–377. Eckblad, M., & Chapman, L. J. (1983). Magical ideation as an indicator of schizotypy. Journal of Consulting and Clinical Psychology, 51, 215–225. Eysenck, H. J., & Eysenck, S. B. G. (1976). Psychoticism as a dimension of personality. London: Hodder and Stoughton. Maier, W., Falkai, P., & Wagner, M. (1999). Schizophrenia spectrum disorders: a review. In M. Maj & N. Sartorius (Eds.), WPA series evidence and experience in psychiatry, Vol. 2, schizophrenia (pp. 311–371). Chichester, UK: Wiley and Sons. Meehl, P. E. (1962). Schizotaxia, schizotypy, schizophrenia. American Psychologist, 17, 827–838. Meyer, T. D., & Hautzinger, M. (1999). Two years stability of psychosis proneness scales and their relations to personality disorder traits. Journal of Personality Assessment, 73, 472–488. Olkin, I. (1967). Correlations revisited. In J. C. Stanley (Ed.), Improving experimental design and statistical analysis (pp. 102–128). Chicago: Rand McNally. Raine, A. (1991). The SPQ: a subscale for the assessment of schizotypal personality based on DSM–III-R criteria. Schizophrenia Bulletin, 17(4), 555–564. Raine, A. (1992). Sex differences in schizotypal personality in a non-clinical population. Journal of Abnormal Psychology, 101, 361–364. Raine, A., Reynolds, C. A., Lencz, T., Scerbo, A., Triphon, N., & Kim, D. (1994). Cognitive perceptual interpersonal and disorganized features of schizotypal personality. Schizophrenia Bulletin, 20, 191–201. Raine, A., Venables, P. H., Mednick, S., & Mellingen, K. (2002). Increased psychophysiological arousal and orienting at ages 3 and 11 years in persistently schizotypal adults. Schizophrenia Research, 54, 77–85.
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Siever, L. J. (1995). Brain structure/function and the dopamine system in schizotypal personality disorder. In A. Raine, T. Lencz, & S. A. Mednick (Eds.), Schizotypal personality (pp. 272–286). New York: Cambridge University Press. Spitzer, R. L., Williams, J. B. W., & Gibbon, M. (1987). Structured clinical interview for DSM-III-R personality disorders: SCID-II. New York: New York State Psychiatric Institute. SPSS (1999). SPSS for Windows, Release 10. Chicago: SPSS Inc. StataCorp (1999). Stata statistical software: Release 6. College Station, TX: StataCorp LP. Stefanis, N. C., Smyrnis, N., Avrampoulos, D., Evdokimidis, I., Ntzoufras, I., & Stefanis, C. N. (2004). Factorial composition of self rated schizotypal traits amongst young males undergoing military training. Schizophrenia Bulletin, 30(2), 335–350. Stefanis, N. C., Van Os, J., Avramopoulos, D., Smyrnis, N., Evdokimidis, I., Hantoumi, I., et al. (2004). Variation in catechol-o-methyltransferase val158 met genotype associated with schizotypy but not cognition: a population study in 543 young men. Biological Psychiatry, 56(7), 510–515. van Os, J., Hanssen, M., Bijl, R. V., & Ravelli, A. (2000). Strauss (1969) revisited: a psychosis continuum in the general population? Schizophrenia Research, 45(1-2), 11–20.
Psychometric properties of the Greek version of the Schizotypal Personality Questionnaire (SPQ) in young male obligatory conscripts: A two years test–retest study Nicholas C. Stefanis a,b,c,*, Silia Vitoratou a,d, Ioannis Ntzoufras d, Nikolaos Smyrnis a,b, Ioannis Evdokimidis a, Costas N. Stefanis a a
University Mental Health Research Institute (UMHRI) 2 Soranou tou Efessiou Str., P.O. Box 66517, 156 01 Papagou, Athens, Greece b Department of Psychiatry, National and Kapodistrian University of Athens, Greece Eginition Hospital, 74 Vas. Sofias Ave., 11528 Athens, Greece c King’s College London, Institute of Psychiatry, Department of Psychological Medicine, London, UK d Department of Statistics, University of Economics and Business, Patision 76, 104 34 Athens, Greece Available online 28 August 2006
Abstract The aim of this paper was the assessment of the psychometric properties of the Greek version of the Schizotypal Personality Questionnaire (SPQ), within the Athens Study of Psychosis Proneness and Incidence of Schizophrenia (ASPIS). The Greek version was administered to 1355 young male conscripts in the Greek Air Force. The Perceptual Aberration Scale (PAS) and Symptom Check List-90-Revised (SCL-90-R) were also included in the study in order to evaluate convergent and discriminant validity. Two years later the SPQ was re-administered to 145 of the conscripts followed by the Structured Interview for DSM-III-R Personality Disorders (SCID-II). The Greek SPQ version replicated the original author’s high internal reliability findings (0.91) providing evidence of convergent (0.70), discriminant (0.32–0.47) and criterion (0.81) validity. The stability estimator of the SPQ was found to be 0.53 while negative schizotypal features appeared to be more stable over time than positive ones. Thirty three percent of the individuals over the 90th percentile of the total SPQ score had a clinical diagnosis of Schizotypal Personality
*
Corresponding author. Address: Department of Psychiatry, National and Kapodistrian University of Athens, Greece Eginition Hospital, 74 Vas. Sofias Ave., 11528 Athens, Greece. Tel.: +30 6932 658067; fax: +30 210 7242020. E-mail address: [email protected] (N.C. Stefanis). 0191-8869/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.paid.2006.07.003
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Disorder (SPD) via the SCID-II interview, while none of the remaining individuals appeared to have this disorder. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Schizotypy; Validity; Reliability; SPD; SPQ; PAS; SCL-90-R; ASPIS
1. Introduction The study of the schizotypal personality traits in apparently normal individuals has received great attention due to genetic and epidemiological studies demonstrating that the schizotypal features cluster in subjects with elevated risk for schizophrenia and prodromal to the subsequent full manifestation of schizophrenia (review by Maier, Falkai, & Wagner, 1999). Two major theoretical approaches exist to explain the link between the schizotypal traits and schizophrenia. The theory of ‘‘schizotaxia’’ of Meehl (1962) proposes that schizotaxia is a conjectured neural integrative defect due to a dominant schizogene that gives rise to the schizotypal personality. This genetic profile implies vulnerability to schizophrenia and in synergy with other polygenic potentiators and adverse life experiences gives rise in a small percentage of these individuals to the clinical syndrome of schizophrenia. Another theoretical approach to schizotypal traits favoured by Eysenck (Eysenck & Eysenck, 1976) states that personality traits such as those that define psychoticism are a continuum from health to schizophrenia with no need to introduce arbitrary cut off points above which schizotypal traits lay as a different entity (Claridge, 1994). According to this view certain dimensions of personality can be found in the general population and their extremes lead to the symptoms of a disease state such as schizophrenia (van Os, Hanssen, Bijl, & Ravelli, 2000). Self-administered questionnaires have been used extensively in several studies examining the schizotypal personality traits. A self-administered questionnaire that assesses all nine aspects of the SPD according to the Diagnostic and Statistical Manual of Mental Disorders Revised DSM-III-R (American Psychiatric Association, 1987) is the Schizotypal Personality Questionnaire (SPQ) developed by Raine (1991). It can be used as a screening instrument in the general population for the identification of individuals with broad schizotypal traits (according to the author, 55% of top SPQ scorers obtained an interview-based SPD diagnosis), and may serve as a measure of individual differences in the schizotypal personality. As part of the ASPIS, the aim of the current study was to assess the psychometric properties of the Greek version of the SPQ in a large unselected sample of apparently healthy young males who are on the one hand at an age of heightened risk for schizophrenia and on the other experiencing a stressful change in life circumstances (Stefanis et al., 2004). 2. Methods 2.1. Participants The translated inventories SCL-90-R (Derogatis, 1993), SPQ and PAS (Chapman, Chapman, & Raulin, 1978) were administered (in this order) to 2243 randomly selected young male conscripts
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aged 18–24 years who were recruited from the Greek Air Force, during their first two weeks of admission in the National Basic Air Force training centre in the city of Tripoli. A team of military medical doctors of all specialties had already evaluated the conscripts as having a satisfactory medical condition, which allowed them to begin their obligatory service. All conscripts signed written consents after agreeing to participate in an anonymous survey. The degree of collaboration was evaluated using the four validity items of the Temperament and Character Inventory (TCI: Cloninger, Przybeck, Svrakic, & Wetzel, 1994). Using this instrument, 832 individuals (37.1%) were traced with disagreement in at least one of the four items (random responders). Scores of the subscales and overall each questionnaire were calculated only for those cases where at least 90% of the items were responded to. Total and subscale SPQ, PAS and SCL-90-R scores are therefore available for 1355, 1354 and 1344 individuals, respectively. After two years, a subsample of the individuals was summoned to participate in a retest analysis at the General Hospital of the Hellenic Air Force (GHHAF).The retest sample constituted of 209 individuals and was reduced to 145 after excluding random responders (23.4%) and individuals with more than the acceptable percentage of missing values (9.4%). For further research purposes the retest sample consisted mainly of individuals who had either scored over the 80th percentile of the total SPQ score in the first assessment (36%) or close to the mean value (40%). 2.2. Instruments The SPQ and PAS were translated into Greek and back translated into English by an independent official translator. Comparison of the original and the first English draft produced a second modified Greek version that received minor further changes. The second back translation was approved by the original questionnaire authors (Raine, A. & Kwapil, T. personal communication, January 1999). A Greek version and standardization of the SCL-90-R in the Greek population can be found in Donias, Karastergiou, and Manos (1991), while reliability analysis is provided in the current paper along with the SPQ and PAS. Furthermore, in order to explore AXIS II psychopathology, re-attenders at the GHHAF were assessed with the Structured Clinical Interview for DSM-III-R personality disorders (SCID-II) (Spitzer, Williams, & Gibbon, 1987) by trained interviewers blind to the self-rated schizotypal status of the conscripts. All data analysis was conducted on the SPSS 10.0 (1999) and STATA 6.0 (1999) statistical packages. 2.3. Analysis 2.3.1. Convergent, discriminant and criterion validity SCL-90-R is a 90-item self-report inventory consisting of nine subscales and three indices of psychological distress. Each subscale assesses symptoms of current psychopathology that do not overlap the SPD symptoms. Hence discriminant validity can be evaluated via the correlation between each SCL-90-R subscale and the SPQ total score. On the contrary, the PAS is a 35-item instrument which taps the perceptual aberration feature of the SPD similarly to the ‘‘Unusual Perceptual Experiences’’ subscale of the SPQ. Hence it can be used to assess convergent validity. Four PAS items (items 6, 13, 24 and 25) were excluded from the analysis due to translation discrepancies that could produce low face validity of the instrument.
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Among the 145 individuals participating in the second assessment of the SPQ at GHHAF, sixteen individuals did not volunteer to participate to the interview process and therefore 129 of the reliable responders on the SPQ finally were evaluated via the SCID-II. The SCID-II assesses all nine traits of the SPD while five have to be present for a positive diagnosis. The 3-point scale (1 indicates that the trait is not present, 2 indicates subthreshold and 3 threshold rating) was used for trait scoring while summing each trait’s score leads to a total SCID-II scoring.
3. Results 3.1. Descriptive indices and internal reliability Descriptive indices and alpha coefficients for the subscales and total SPQ are presented in Table 1 for the first assessment sample (along with the corresponding indices for the random responders whose missing values were not exceeded by 20% of the SPQ items: 420 individuals). The lower and upper cut off scores (ten-tiles) of the total SPQ scores were found equal to 12 and 44, respectively. Cronbach’s alpha coefficient was high (0.91) for the total score and satisfactory for the subscales (0.58–0.80). Seven problematic items were traced (6, 28, 33, 37, 49, 62 and 65) with low item-total correlations (lower than 0.20) and no decrease of alpha at item deletion. However, only item 49 was problematic within its corresponding scale. The SPQ scores were found to correlate negatively with age (r = 0.18, p < 0.001). The internal consistency of the PAS was also found to be satisfactory with alpha being equal to 0.88. The mean PAS score was 5.17 (n = 1354, median = 4.00, SD = 5.24) while the values ranged from 0 to 30. The distribution of PAS scores was skewed (1.55) and the lower and upper cut off ten tiles were equal to zero and twelve, respectively. No problematic items were traced since the item total correlations were ranged from 0.28 to 0.50.
Table 1 Descriptive indices and alpha coefficients for subscales and total SPQ, first assessment sample (n = 1355)a SPQ subscale
Alpha
Ideas of reference Social Anxiety Odd Beliefs/Magical Thinking Unusual Perceptual Experiences Odd Behaviour and Appearance No Close Friends Odd Speech Constricted Affect Suspiciousness/Paranoid Ideation
0.66 0.76 0.58 0.72 0.80 0.58 0.73 0.63 0.69
Total Score
0.91 (0.90)
*
(0.57) (0.67) (0.57) (0.68) (0.65) (0.61) (0.57) (0.60) (0.61)
Mean *
SD
Range
4.98 (4.61) 3.20* (3.49) 1.98* (2.45) 2.61* (3.30) 2.75* (3.05) 2.29* (3.26) 3.85 (3.97) 2.12* (2.97) 3.75 (3.93)
2.10 2.30 1.62 2.17 2.24 1.80 2.41 1.80 2.06
(2.01) (2.19) (1.75) (2.24) (1.95) (2.06) (2.09) (1.93) (1.97)
27.78* (31.09)
12.35 (12.34)
0–9 0–8 0–7 0–9 0–7 0–9 0–9 0–8 0–8 0–68
The scores between reliable and random responders were statistically different according t-test (p < 0.05). Within parentheses are presented the corresponding descriptive indices for the random responders with less than 50% missing values (n = 410). a
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The overall subscale alpha coefficient was also high (0.97) in the case of the SCL-90-R, while the corresponding coefficients for each subscale were found to range from 0.66 to 0.87. The item total correlations ranged from 0.28 to 0.60, so no problematic items were traced. 3.2. Test–retest reliability The stability of the total SPQ score was moderate with the Pearson correlation being equal to 0.53 (p < 0.001). The lowest test–retest coefficients were calculated for the subscales that assess the positive features of the SPD and the highest for the subscales that assess those that are negative. There were no significant differences (z-based Pearson-Filon: ZPF, Dunn & Clark, 1969) within the coefficients of the subscales for the positive features while they were significantly lower than the coefficients for those that are negative with the exception in the ‘‘No close friends’’ subscale (Table 2). Furthermore, a severe decrease in the subscale (34.8–68.4%) and total SPQ (48.1%) scores was present. The differences in the decreases were tested (adjusting subscale scores for the number of items included) but no particular pattern became apparent since the statistically significant differences were randomly distributed among the subscales. 3.3. Convergent and discriminant validity The correlation between the PAS and the SPQ subscale of ‘‘Unusual Perceptual Experiences’’ was found to be satisfactory (0.70), while the correlations between the PAS and the rest of the SPQ subscales were much lower ranging from 0.32 to 0.45 (Table 3). The correlation between the total SPQ score and each of the nine subscales of the SCL-90-R ranged from 0.35 to 0.47. Furthermore, the correlations between both SPQ and SCL-90-R subscales were found to be lower than 0.45 (p < 0.001, in all cases). Each coefficient between the PAS score and SPQ subscales and between the subscales of the SPQ and the SCL-90-R was significantly lower than the
Table 2 Test–retest reliability and mean difference on SPQ scores, between assessment samples (n = 145) SPQ subscalea
Test–retest coefficient*,b N2,N3,D1,D2
P1. Unusual Perceptual Experiences P2. Ideas of reference P3. Odd Beliefs/Magical Thinking PN. Suspiciousness/Paranoid Ideation N1. No Close Friends D1. Odd Behaviour and Appearance D2. Odd Speech N2. Constricted Affect N3. Social Anxiety
0.29 0.32N2,N3,D2 0.35N2,N3,D2 0.37N2,N3,D2 0.41N3,D2 0.45N2,N3,P1 0.51P1,P2,P3,PN 0.58P1,P2,P3,PN,N1,D1 0.62P1,P2,P3,PN,N1,D1
Total Score
0.53
*
Mean score difference*
%
2.23 3.26 1.21 1.85 1.14 1.80 2.07 0.98 1.81
68.4 56.4 51.6 40.2 40.7 51.2 42.2 34.8 44.6
16.48
48.1
p < 0.001. P: positive, N: negative, D: disorganized feature. b The superscripts notify the id of the subscales with significantly different (p < 0.05) test–retest coefficients according ZPF. a
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Table 3 Correlations of SPQ subscales and total scores with convergent/discriminant validity subscales (first assessment sample, n = 1355) SCL-90-R subscale
SPQ total score* r
SPQ subscale
PAS score* r
Anxiety Depression Phobic Anxiety Hostility Interpersonal Sensitivity Obsessive-Compulsive Paranoid Ideation Psychoticism Somatization
0.47 0.47 0.42 0.35 0.42 0.46 0.39 0.42 0.37
Ideas of reference Social Anxiety Odd Beliefs/Magical Thinking Unusual Perceptual Experiences Odd Behaviour and Appearance No Close Friends Odd Speech Constricted Affect Suspiciousness/Paranoid Ideation
0.40 0.32 0.43 0.70 0.43 0.38 0.45 0.43 0.38
*
All correlation coefficients were statistically significant (p < 0.0001).
correlation between the PAS and the ‘‘Unusual Perceptual Experiences’’ subscale (Olkin, 1967, z for comparing dependent correlation coefficients, p < 0.001 in all cases). 3.4. Criterion validity From the total of the 129 valid retest cases interviewed with the SCID-II, 9 and 13 individuals were identified as high and low (respectively) SPQ scorers. Among the 9 individuals with a high SPQ score, three (33.3%) received a clinical diagnosis of the SPD while none of the remaining 120 individuals received such a diagnosis. This subsample that consists of the 22 high and low scorers was studied following Raine’s (1991) initial study. The clinical diagnosis of the SPD (positive/negative) was found to have positive but moderate associations with both group membership (high/ low; phi = 0.48, p = 0.025) and the SPQ total scores (point bi-serial r = 0.51 p = 0.016). The Spearman correlations between both SPQ scores and SCID-II ratings (Table 4) were moderate to high (0.38–0.90). For six of the subscales, the correlations were statistically significant while the other two were marginally significant (p < 0.10). In the case of ‘‘Odd Behaviour and Appearance’’ the SCID-II score was zero for all individuals and no correlation could be calculated. Total SPQ score was highly correlated with the SCID over-all-traits score (rSpearman = 0.81, p < 0.001). Furthermore, t-tests for two independent samples indicated that the mean score of the SPQ subscales were significantly higher (p < 0.05) when the trait was present, with the exception of the ‘‘Odd Speech’’ subscale where the mean difference was evidential of a trend (p = 0.114), even though the mean was higher in the trait present group. Among the 6 high scorers that did not receive a clinical diagnosis on the SPD, one individual did not show any SPD symptoms, while 4 others were rated with one or two subthresholds plus at least two threshold ratings. One further individual reached the threshold of the diagnosis by having four traits. The 120 individuals that did not meet the higher cut off score had significantly lower SCID-II over-all-traits scores (mean difference = 4.83, SD = 1.32, p < 0.0001). Apart from the retest subsample of the high and low scorers, the entire sample of the 129 individuals was also considered in this study. Using logistic regression, the odds ratio (OR) of receiv-
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Table 4 Correlations between SPQ scores and SCID-II ratings for each trait and total (second assessment subsample of high/ low scorers, n = 22) SPQ subscale
SCID-II interview r
1. 2. 3. 4. 5. 6. 7. 8. 9.
0.79* 0.90* 0.56* 0.40** – 0.52* 0.38** 0.65* 0.65*
Ideas of reference Social Anxiety Odd Beliefs/Magical Thinking Unusual Perceptual Experiences Odd Behaviour and Appearance No Close Friends Odd Speech Constricted Affect Suspiciousness/Paranoid Ideation
0.81*
Total Score * **
p < 0.05. p < 0.10.
ing a clinical diagnosis on the SPD via the SPQ score increment was calculated to be 1.27 (p = 0.011). Applying ordinal logistic regression (Table 5) at the 3-point rating of the SCID-II for each trait by score increment in the SPQ subscales, the ORs varied from 1.56 to 2.55. In the case of the ‘‘Odd Speech’’ the estimated OR was not significant (p = 0.450). The proportional-odds assumption was not violated in any model. 3.5. Factor structure The analysis of the factorial structure of the SPQ as defined by the responses of the 1355 conscripts can be found in Stefanis et al. (2004). Confirmatory factor analysis indicated that the three factor model (Cognitive/Perceptual, Disorganized and Interpersonal factor) suggested by Raine
Table 5 Odds ratios of receiving a SPD diagnosis by score increment in the SPQ subscales and total scores (second assessment sample, n = 129) SPQ subscale 1. 2. 3. 4. 5. 6. 7. 8. 9. * **
Ideas of reference Social Anxiety Odd Beliefs/Magical Thinking Unusual Perceptual Experiences Odd Behaviour and Appearance No Close Friends Odd Speech Constricted Affect Suspiciousness/Paranoid Ideation p < 0.001. p = 0.448.
OR
SE *
1.83 2.55* 1.97* 1.80* – 2.02* 1.10** 2.00* 1.56*
0.23 0.45 0.37 0.32 – 0.39 0.14 0.38 0.20
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Ideas of Reference
Cognitive Perceptual
Odd Beliefs Perceptual Experiences
Paranoid Suspiciousness Social Anxiety Negative No Close Friends Constricted Affect Disorganization Odd Behaviour Odd Speech
Fig. 1. Path representation of the proposed four-factor model (Stefanis et al., 2004). Table 6 Descriptive indices and alpha coefficients for the three factors model (first assessment sample, n = 1355) SPQ Factor
Alpha
Mean
SD
Range
1. Interpersonal 2. Cognitive-Perceptual 3. Disorganized
0.83 0.83 0.85
11.48 13.43 6.60
6.01 5.99 4.08
0–32 0–33 0–16
et al. (1994) provided a good fit to the data. However, better fit to the data was provided by a four factor model where positive schizotypy is further divided into a paranoid and a cognitive-perceptual factor (Fig. 1). The descriptive indices and alpha coefficients of the three sum-factors (summing the raw scores of the respective subscales) suggested by Raine et al. (1994), are given in Table 6.
4. Discussion The primary aim of this study was to assess the reliability and validity of the Greek version of the SPQ. Further, the psychometric indices of the PAS and SCL-90-R scales were estimated concurrently. In the first assessment sample three of the SPQ subscales had moderate alpha coefficients (0.58–0.63) and noticeably lower than the corresponding ones in Raine’s samples (Table 1). Furthermore, the item 49 (writing letters to friends is more trouble than it is worth) had low item-scale correlation with ‘‘no close friends’’. However the restricted age range of our sample may explain this, since more direct types of communication (such as mobile phone calls) are preferred by individuals of this age.
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As Raine, Venables, Mednick, and Mellingen (2002, p. 77), point out it is possible that ‘‘while some individuals are persistently schizotypal over time, some others change their status’’, even though it is commonly believed that schizotypal personality features remain stable throughout life. Indeed the stability of the SPQ subscales scores was found in this study to be low to moderate (0.29–0.62) for a time period of two years. It is possible then that several high scorers on schizotypal tests are ‘‘pseudo-schizotypals’’ receiving low scores in later studies. These values are comparable with the two years test–retest reliability estimators reported for the PAS and the Magical Ideation Scale (Eckblad & Chapman, 1983) by Meyer and Hautzinger (1999). As can be seen in Table 2, the lowest test–retest coefficients appear in the positive schizotypy dimension (0.29–0.35), the subscales referring to the ‘‘Disorganized factor’’ lie in between, while the negative features appear to be less affected during the 2 year time interval period (0.41–0.62). Negative schizotypy as a construct appears to be more stable over time than positive, adding to the accumulating evidence that schizotypal dimensions are influenced by somewhat different underlying genetic, pathophysiological and environmental processes (Siever, 1995; Stefanis et al., 2004). The subscale and total norms of the SPQ for the first assessment sample are similar to the corresponding ones of the American population as provided by Raine (1991), with analogous high and low cut off points. However, in the second assessment results a severe decrease in scores was present (34.8–68.4%). This generalized reduction in SPQ subscales at the retest time point (end of military training) can be attributed to the absence of environmental stressful circumstances that existed during the first assessment (stress associated with initiation of compulsory military service) and indicates that psychometrically defined schizotypal personality traits may be much more sensitive to environmental stressors than previously thought of. Finally, since age correlates negatively with the SPD features, the long time elapsed additionally justifies the lower scores. The SPQ demonstrated low correlations with the subscales that do not measure schizotypal features and high ones with the PAS evidencing discriminant and convergent validity, respectively. A high correlation between the PAS and the SPQ subscale of the ‘‘Unusual Perceptual Experiences’’ was found (0.70). Furthermore, the correlations between the PAS and the rest of the SPQ subscales were significantly lower and moderate in magnitude, ranging from 0.32 s0 0.45, indicating discriminant validity. Moreover, these results can be considered as confirmative of the PAS validity. This fact, in addition with the high internal consistency of the scale, demonstrates the good psychometric properties of the PAS Greek version (not including however items 6, 13, 24 and 25). Evidence in favour of the discriminant validity of SPQ were also provided by the correlations between the SPQ total and subscales scores and each of the nine subscales of the SCL-90-R ranging from low to moderate (0.35–0.47). All correlations between the SPQ and the discriminant subscales were significantly lower than the correlation used for convergent validity assessment. These validity estimators are comparable with the analogous ones in the American population provided by Raine (1991). During the second application of the SPQ in GHHAF, 129 of the 145 individuals also participated to a clinical evaluation via a SCID-II interview in order to assess criterion validity. Three individuals were found to meet the DSM-III-R criteria for the SPD. All three individuals had scored above the high cut-off score in the distribution of the SPQ total score at both time points. This yields an estimation of 33.3% of the high scorers expected to have this disorder. Since 5 high scorers of the initial retest sample of the 145 individuals were not interviewed, this percentage is
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only suggestive of the positive predictive value of the high cut off score criterion. Moreover, the individuals in the upper SPQ ten-tile with no SPD diagnosis, were found to have a substantial number of subthreshold or threshold ratings via the SCID-II interview. These results confirm that high SPQ scores are suggestive of SPD. The subsample that consists of the 22 high and low scorers yielded moderate to high positive correlations between each SPQ subscale score and the corresponding SCID-II rating, while the SPQ subscale scores were significantly higher for individuals with subthreshold or threshold ratings versus individuals that didn’t receive such a diagnosis for a specific trait. In addition, total SPQ scores were highly correlated with the SCID over-all-traits score (0.81) confirming that high SPQ scores evince individuals with at least a substantial number of subthreshold or threshold ratings. This is further indicated by the fact that the high scorer’s group had significantly higher SCID over-all-traits scores than the low scorers’ group. The positive association between the SPQ score and SPD symptoms is therefore confirmed by the current study, replicating Raine’s findings. The differences in the odds of receiving a SPD diagnosis by the increment of the SPQ scores were calculated for the entire second assessment subsample of the 129 individuals who concurrently assessed the SPQ and received a clinical evaluation via the SCID-II. The OR of receiving a SPD diagnosis (1.27) indicates that for each increment of the total SPQ score by positive item response, the odds to receive a SPD diagnosis increase by 27%. The difference in the odds of receiving a subthreshold or threshold rating of a particular trait by the SPQ score increment is even steeper. Under the proportional odds assumption it is hypothesized that a latent continuum lies beneath the three points SCID-II rating and regardless of the dichotomization of this rating for a particular trait, the OR is constant. Hence, the percent increment in the odds of receiving at least a subthreshold rating for a particular trait by positive item response on the corresponding subscale equals the expected increment in the odds of receiving at most subthreshold ratings (versus receiving threshold rating) and varies from 56% to 155% (Table 5). These estimations confirm that higher SPQ scores are robustly suggestive either of SPD or at least of the presence of particular traits at subscale level. Furthermore, confirming Raine’s (1991) hypothesis, none of the individuals beyond the high scorers’ group received a positive diagnosis. This indicates that the use of the 10% high cut-off score can be considered as a sensitive criterion in tracing individuals in normative populations with a potential SPD diagnosis.
5. Methodological limitations Our sample consisted of young males that were recruited in the military service. Thus it cannot be claimed that our findings could be directly generalized to the Greek population (men and women of every age). Both age and gender are consistently reported to modify the SPD measurements. In particular, age is reported to be negatively correlated with the SPQ scores while males score significantly higher on negative symptom subscales than females and significantly lower on positive ones (Raine, 1992). However, this sample can be considered representative of males in this age, since military service is obligatory in Greece. The high percentage of random responders in the study is attributed possibly to gains related to avoidance of military drills during the day of examination and subsequent indifference during
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testing procedures, and not due to genuine psychometrically deviant performance. Such an explanation is plausible since, even though the random responders had significantly augmented schizotypal scores compared to correct responders (Table 2), they exhibited significantly higher avoidance and escape patterns (SCL-90-R Phobic anxiety: mean difference = 0.12, p = 0.001) while not differing from correct responders in other SCL-90-R state psychopathology such as paranoid ideation, psychoticism, or depression (p > 0.05). The second assessment sample consisted mainly of high and moderate scorers of the first assessment sample. This might introduce some bias, even though all categories of scorers were represented (at least 3 individuals from each ten-tile of the first assessment). Moreover no analysis was performed to assess the degree of agreement between the interviewers of the SCID-II. Further information concerning the high percentage of random responders can be found in Stefanis et al. (2004).
References American Psychiatric Association (1987). DSM-III R: Diagnostic and statistical manual of mental disorders (3rd ed. revised). Washington, DC: APA. Chapman, L. J., Chapman, J. P., & Raulin, M. L. (1978). Body—image aberration in schizophrenia. Journal of Abnormal Psychology, 87, 399–407. Claridge, G. S. (1994). Single indicator of risk for schizophrenia: probable fact or likely myth? Schizophrenia Bulletin, 20, 151–168. Cloninger, C. R., Przybeck, T., Svrakic, D., & Wetzel, R. (1994). The Temperament and Character Inventory (TCI): A guide to its development and use. St. Louis, Missouri: Washington University, Centre for Psychobiology of Personality. Derogatis, L. R. (1993). Symptom Checklist-90-R (SCL-90-R). Minneapolis, MN: Computer Systems, Inc. Donias, S., Karastergiou, A., & Manos, N. (1991). Standardization of the symptom check-list-90-R rating scale in a Greek population. Psychiatriki, 2, 42–48. Dunn, O. J., & Clark, V. A. (1969). Correlation coefficients measured on the same individuals. Journal of the American Statistical Association, 64, 366–377. Eckblad, M., & Chapman, L. J. (1983). Magical ideation as an indicator of schizotypy. Journal of Consulting and Clinical Psychology, 51, 215–225. Eysenck, H. J., & Eysenck, S. B. G. (1976). Psychoticism as a dimension of personality. London: Hodder and Stoughton. Maier, W., Falkai, P., & Wagner, M. (1999). Schizophrenia spectrum disorders: a review. In M. Maj & N. Sartorius (Eds.), WPA series evidence and experience in psychiatry, Vol. 2, schizophrenia (pp. 311–371). Chichester, UK: Wiley and Sons. Meehl, P. E. (1962). Schizotaxia, schizotypy, schizophrenia. American Psychologist, 17, 827–838. Meyer, T. D., & Hautzinger, M. (1999). Two years stability of psychosis proneness scales and their relations to personality disorder traits. Journal of Personality Assessment, 73, 472–488. Olkin, I. (1967). Correlations revisited. In J. C. Stanley (Ed.), Improving experimental design and statistical analysis (pp. 102–128). Chicago: Rand McNally. Raine, A. (1991). The SPQ: a subscale for the assessment of schizotypal personality based on DSM–III-R criteria. Schizophrenia Bulletin, 17(4), 555–564. Raine, A. (1992). Sex differences in schizotypal personality in a non-clinical population. Journal of Abnormal Psychology, 101, 361–364. Raine, A., Reynolds, C. A., Lencz, T., Scerbo, A., Triphon, N., & Kim, D. (1994). Cognitive perceptual interpersonal and disorganized features of schizotypal personality. Schizophrenia Bulletin, 20, 191–201. Raine, A., Venables, P. H., Mednick, S., & Mellingen, K. (2002). Increased psychophysiological arousal and orienting at ages 3 and 11 years in persistently schizotypal adults. Schizophrenia Research, 54, 77–85.
1286
N.C. Stefanis et al. / Personality and Individual Differences 41 (2006) 1275–1286
Siever, L. J. (1995). Brain structure/function and the dopamine system in schizotypal personality disorder. In A. Raine, T. Lencz, & S. A. Mednick (Eds.), Schizotypal personality (pp. 272–286). New York: Cambridge University Press. Spitzer, R. L., Williams, J. B. W., & Gibbon, M. (1987). Structured clinical interview for DSM-III-R personality disorders: SCID-II. New York: New York State Psychiatric Institute. SPSS (1999). SPSS for Windows, Release 10. Chicago: SPSS Inc. StataCorp (1999). Stata statistical software: Release 6. College Station, TX: StataCorp LP. Stefanis, N. C., Smyrnis, N., Avrampoulos, D., Evdokimidis, I., Ntzoufras, I., & Stefanis, C. N. (2004). Factorial composition of self rated schizotypal traits amongst young males undergoing military training. Schizophrenia Bulletin, 30(2), 335–350. Stefanis, N. C., Van Os, J., Avramopoulos, D., Smyrnis, N., Evdokimidis, I., Hantoumi, I., et al. (2004). Variation in catechol-o-methyltransferase val158 met genotype associated with schizotypy but not cognition: a population study in 543 young men. Biological Psychiatry, 56(7), 510–515. van Os, J., Hanssen, M., Bijl, R. V., & Ravelli, A. (2000). Strauss (1969) revisited: a psychosis continuum in the general population? Schizophrenia Research, 45(1-2), 11–20.