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Gender differences in schizotypal personality in a Chinese population
Personality and Individual Differences 50 (2011) 404–408
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Gender differences in schizotypal personality in a Chinese population Meng En Guo a,⇑, Simon Lowes Collinson a,b, Mythily Subramaniam a, Siow Ann Chong a a b
Research Division, Institute of Mental Health/Woodbridge Hospital, 10 Buangkok View, Singapore 539747, Singapore Department of Psychology, Faculty of Arts and Social Sciences, National University of Singapore, Block AS54, #02-07, 9 Arts Link, Singapore 117570, Singapore
a r t i c l e
i n f o
Article history: Received 27 June 2010 Received in revised form 29 October 2010 Accepted 2 November 2010 Available online 23 November 2010 Keywords: Schizophrenia Schizotypal personality traits Schizotypy SPQ Gender
a b s t r a c t Studies that have examined schizotypal personality traits using self-reported measures have found gender differences in the expression and degree of schizotypy. Despite the reported presence of schizotypal traits in Asian populations, putative gender differences have been almost entirely derived from studies of Western populations. This study examined the gender effect of schizotypy in a broad sample of the Chinese population in Singapore using the Schizotypal Personality Questionnaire (SPQ). The questionnaire was administered to 538 (308 males and 230 females) subjects (age range of 21–55). As with previous studies, gender differences were related to the presence of negative schizotypal personality traits, namely No Close Friends and Constricted Affect. The spectrum of differences in schizotypy was also extended to the psychosocial sphere as marital status and years of education were significantly associated with several SPQ domains. The findings suggest that there are common elements in Asian and Caucasian populations and that psychosocial risk is an important correlate of schizotypy. The implications of gender differences in the aetiology of schizophrenia spectrum disorders are discussed. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Research examining the spectrum of schizotypal personality within general populations has increased rapidly in recent years (Raine, 2006). Because trait-like features are present in individuals with or without Schizotypal Personality Disorder who are at heightened genetic risk for schizophrenia, examining schizotypy within general populations provides a means to examine biological and cognitive markers of schizophrenia without the confounding effects of severe psychotic symptoms (Raine & Lencz, 1995). There is evidence to suggest gender differences in the expression of symptoms in schizophrenia and may be important in the aetiology of the disorder (Castle, Abel, Takei, & Murray, 1995; Castle & Murray, 1991; Leung & Chue, 2000). Men with schizophrenia have an earlier onset, tend to have more negative symptoms and poorer psychosocial functioning. Women, on the other hand, are characterized by greater affective and paranoid symptoms and fewer functioning deficits (Goldstein & Link, 1988; Leung & Chue, 2000). Gender differences are also found in relation to schizotypal personality. Miettunen and Jaaskelainen’s (2010) meta-analysis on the Wisconsin Schizotypy Scales found that males are characterized by
⇑ Corresponding author. Tel.: +65 63893611. E-mail address: [email protected] (M.E. Guo). 0191-8869/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.paid.2010.11.005
higher scores on ‘negative’ schizotypal personality traits of social isolation with Physical Anhedonia and Social Anhedonia and in previous single studies on Schizotypal Personality Questionnaire (SPQ), males are found to score higher on No Close Friends and Constricted Affect (Badcock & Dragovic, 2006; Bora & Arabaci, 2009; Ma et al., 2007; Miller & Burns, 1995; Raine,1992), whilst several SPQ studies suggest that women are higher on ‘positive’ schizotypal personality traits - having higher rates of Ideas of Reference and Odd Beliefs/Magical Thinking (Badcock & Dragovic, 2006; Bora & Arabaci, 2009; Raine,1992; Roth & Baribeau, 1997). In contrast, conflicting findings have been reported by Roth and Baribeau (1997) and Ma et al. (2007) with male subjects reporting elevated rates of ‘positive’ schizotypal personality traits of eccentric/odd behavior, and Miller and Burns (1995) also did not find higher rates of ‘positive’ schizotypal personality traits in female subjects, whereas Miettunen & Jaaskelainen’s (2010) meta-analysis suggests there may be no difference between males and females in positive symptoms. In order to establish the validity of the Schizotypal Personality Questionnaire (SPQ) on Singapore Asian populations and further examine the gender effect of schizotypy in Asian subjects, we examined SPQ in a broad sample of the Chinese population of Singapore. As there are conflicting findings regarding the rates of negative and positive symptoms between males and female and based on the findings of several SPQ studies, the hypothesis of this study is that Asian men would score higher on ‘negative’ schizotypal personality traits and women would score higher on ‘positive’ schizotypal personality traits.
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2. Methods 2.1. Subjects Singapore is an island state in Southeast Asia with a multi-racial population of about 4.5 million. Those of Chinese descent (75.2%) constitute the majority of the population, follow by the Malays (13.6%), Indians (8.8%) and Eurasians and other groups (2.4%).This study was carried out in the country’s only state mental health treatment facility and it was a part of a larger study aimed at elucidating the genetic vulnerability or neurocognitive endophenotypes in schizophrenia. The study was approved by the relevant institutional ethics and review board – the National Healthcare Group Domain-Specific Review Boards (DSRB). All subjects were recruited from the community through advertisements. The subjects were of Chinese ethnicity aged between 21–55 years old, able to understand spoken English, completed at least 6 years of formal education and had no significant history of alcohol or drug abuse. Subjects were screened with the Structured Clinical Interview for DSM-IV Axis I disorders - Non-patient edition (SCID-I/NP; First, Spitzer, Gibbon, & Williams, 2007) to ensure that they did not have a history of psychiatric disorder or psychotic symptoms. The Schizotypal Personality Questionnaire (SPQ; Raine, 1991) was administered to all the subjects in individual sessions. All subjects gave written informed consent.
Social Anxiety, No Close Friends, Constricted Affect and Paranoid Ideation make up the Interpersonal Deficits factor. The third factor i.e. Disorganised deficits is composed of Odd Behavior and Speech. The scale was reported to have sound psychometric properties with high internal reliability (0.91), high test–retest reliability (0.82), convergent validity (0.59 to 0.81), discriminant validity (0.63) and criterion validity (0.68) (Raine, 1991).
2.3. Statistical analysis All statistical analyses were performed with SPSS 18.0 for Windows (SPSS, Chicago, USA). Statistical significance was set at p < .05. Descriptive statistics including mean and standard deviation (SD) for continuous variables, and frequency and percentages for categorical variables were computed to explore sociodemographics variables of the study sample. Independent sample t-tests were used to compare the means scores of all SPQ domains (SPQ total score, nine subscales and three factors) and continuous demographic variables between the males and females. Chi-square tests were used to test the categorical variables. Separate hierarchical multiple regressions were conducted for each SPQ component. Demographic variables, age, smoking habit, marital status, living status, education level, total years of education and occupation status were entered as control covariates in model 1 and gender was entered into model 2. Cronbach’s alpha was also conducted to explore the internal consistency of the nine SPQ subscales.
2.2. Measures The SPQ is a 74-item self-rated scale to assess all nine traits of Schizotypal Personality Disorder (SPD) listed in the DSM-III-R. The SPQ comprises yes/no items and the total score ranges from 0 to 74. The nine subscales can be computed using the summation of corresponding items and the three main factors, Cognitive-Perceptual Dysfunction, Interpersonal deficits and Disorganised deficits as outlined in the DSM, can be computed using summation of the corresponding subscales scores. Cognitive-Perceptual Deficits factor is the summation of Ideas of reference, Odd Beliefs / Magical Thinking, Unusual Perceptual Experiences and Paranoid Ideation.
3. Results 3.1. Descriptive statistics In all, 538 subjects were recruited for this study and the sample comprised 308 (57.2%) males and 230 (42.8%) females. The mean age of the subjects was 31.4 years (SD = 10.7), their mean years of education was 13.7 years (SD = 2.5), and most (N = 309, 58.1%) had high school, tertiary education, or technical education below university level. The majority of the subjects were not married
Table 1 Demographics characteristics comparison between males and females. Characteristics
Males (n = 308) Mean
Age (years) Education (years)
a b c
28.61 13.84
Females(n = 230) SD 9.22 2.11
Mean 35.13 13.46
Statistic
11.48 2.84
N
%
N
%
Education level Lowa Mediumb Highc
37 205 64
12.09 66.99 20.92
59 104 63
26.11 46.02 27.88
Marital status Married/had a partner Not married
63 245
20.45 79.55
102 128
44.30 55.65
Occupation status Employed Not employed/homemaker/retired Student
148 22 136
48.37 7.19 44.44
156 32 42
67.83 13.91 18.26
Smoking status Smoker Non smoker
48 260
15.60 84.42
15 215
6.50 93.50
Living status Self With others
10 298
3.25 96.75
4 225
1.75 98.25
Primary or secondary school level. High school, tertiary education, or technical education below university level. University level or above.
p
SD t = 7.07 t = 1.70
<.001 0.091
v2 = 26.64
<.001
v2 = 35.35
<.001
v2 = 41.77
<.001
v2 = 10.46
.001
v2 = 1.16
.281
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M.E. Guo et al. / Personality and Individual Differences 50 (2011) 404–408
Table 2 Schizotypal personality traits comparison between males and females. Variable
Males (n = 308)
SPQ total score Ideas of Reference Excessive Social Anxiety Odd Beliefs/Magical Thinking Unusual Perceptual Experiences Odd Behavior No Close Friends Odd Speech Constricted Affect Suspiciousness/Paranoid Cognitive-Perceptual Factor Interpersonal Factor Disorganised Factor
Females (n = 230)
a
Mean
SD
a
Mean
SD
.88 .87 .87 .88 .88 .87 .87 .87 .87 .87 .85 .85 .86
13.11 1.76 2.08 1.23 0.51 0.64 1.83 2.17 1.42 1.48 4.98 6.81 2.81
10.11 1.87 1.97 1.34 0.85 1.21 2.03 2.06 1.71 1.56 4.30 5.98 2.86
.88 .87 .87 .87 .87 .87 .87 .87 .87 .87 .85 .85 .86
10.67 1.46 1.85 1.15 0.44 0.53 1.36 1.75 0.86 1.27 4.32 5.34 2.28
8.67 1.61 1.82 1.35 0.89 1.22 1.65 1.74 1.29 1.40 4.08 4.79 2.59
Statistic
p
t = 3.01 t = 1.96 t = 1.40 t = 0.73 t = 0.94 t = 1.00 t = 2.96 t = 2.57 t = 4.33 t = 1.61 t = 1.80 t = 3.16 t = 2.20
.003 .051 .162 .464 .350 .318 .003 .010 <.001 .108 .073 .002 .028
Table 3 Hierarchical regression coefficients for total score, the subscales of No Close Friends, Constricted Affect, Suspiciousness/Paranoid, Ideas of Reference, Odd Behavior and three factors of the Schizotypal Personality Questionnaire. Variable (regression 1)
Total score
DR 2 Step 1 Step 2 Age (years) Smoking status Living status Education (years) Educationa (medium level) Educationa (high level) Occupationb (employed) Occupationb (student) Marital status Gender Variable (regression 2)
0.045 0.005
Variable (regression 3)
Step 1 Step 2 Age (years) Smoking status Living status Education (years) Educationa (medium level) Educationa (high level) Occupationb (employed) Occupationb (student) Marital status Gender
Constricted Affect p
b
0.034 0.013 0.007 0.127 0.152 0.123 0.113 0.071 0.131 0.108
0.017 0.002
DR2
0.013 0.047 0.008 0.086 0.043 0.043 0.028 0.006 0.157 0.063
0.039 0.007
DR2
.904 .408 .242 .215 .159 .192 .236 .846 .025 .052
p
b
0.058 0.050 0.019 0.087 0.061 0.017 0.020 0.002 0.202 0.006
.399 .253 .675 .177 .436 .847 .788 .984 .000 .895
Disorganised Factor p
b
0.029 0.002 0.008 0.036 0.052 0.080 0.111 0.116 0.087 0.016 0.129 0.090
DR2
.845 .283 .854 .186 .583 .630 .699 .943 .007 .173
Cognitive Perceptual Factor p
b
.324 .188 .143 .219 .295 .478 .552 .630 .082 .001
0.042 0.000
.773 .293 .512 .710 .372 .338 .534 .633 .048 .327
Interpersonal Factor
0.067 0.058 0.065 0.079 0.082 0.063 0.043 0.040 0.100 0.148 Odd Behavior
p
b
0.030 0.003 0.020 0.047 0.030 0.024 0.071 0.086 0.046 0.040 0.116 0.046
p
b
.615 .765 .866 .049 .054 .165 .122 .392 .024 .020
Idea of Reference p
b
DR2 0.032 0.019
.775 .438 .276 .374 .270 .195 .762 .879 .004 .089
Suspiciousness/Paranoid
DR 2
DR2 0.033 0.010
0.019 0.034 0.048 0.057 0.087 0.114 0.022 0.013 0.168 0.078
DR 2 Step 1 Step 2 Age (years) Smoking status Living status Education (years) Educationa (medium level) Educationa (high level) Occupationb (employed) Occupationb (student) Marital status Gender
No Close Friends p
b
DR2
p
b
0.043 0.001 0.008 0.017 0.043 0.007 0.058 0.100 0.053 0.001 0.160 0.052
.909 .707 .335 .916 .463 .264 .470 .988 .006 .261
0.061 0.045 0.014 0.062 0.028 0.059 0.009 0.031 0.143 0.036
.369 .304 .761 .339 .721 .502 .900 .705 .013 .432
Note: Change in R2 values indicate the association significance test for change in R2 as each block of variables is entered into the model. Step 2 is controlled with age, smoking status, living status, education, occupation and marital status. Not reported in this table are the subscales of Odd Beliefs/Magical Thinking, Unusual Perceptual Experiences, Excessive Social Anxiety and Odd Speech which do not reveal any significant association. a Education (low level) as the reference group. b Occupation (unemployed/homemakers/retired) as the reference group.
M.E. Guo et al. / Personality and Individual Differences 50 (2011) 404–408
(N = 373, 69.3%), non-smokers (N = 475, 88.3%), employed (N = 304, 56.7%) and living with someone (N = 523, 97.4%). Table 1 presents the comparison of the demographics characteristics between the males and females. Males were more likely to be single, younger, smokers, students and with education above secondary level compared with the females. There were no significant differences in years of education and living status between males and females. The internal consistency of each SPQ subscale was high (Cronbach’s a range = 0.81–0.85) and independent sample t-tests revealed that males had higher scores than females in all the SPQ domains (Table 2). Males displayed significantly higher scores on the SPQ total score (p = .003), the negative subscales of No Close Friends (p = .003), Constricted Affect (p<.001) and the positive subscale of Odd Speech (p = .010). They also scored higher on the Interpersonal (p = .002) and Disorganised (p = .028) factors. No other significant gender differences were observed on other SPQ domains. 3.2. Hierarchical multiple regression analyses Table 3 illustrates the results of hierarchical multiple regression analyses and shows that gender differences remained significant in the following domains: No Close Friends (p = .020) and Constricted Affect (p = .001) with males scoring higher on both scales. However, the differences were not observed in the SPQ total score, Odd Speech, Disorganised and Interpersonal as reported in the univariate analyses. As reported in model 2 of No Close Friends, gender contributed an additional 1% variance in the score. Marital status (p=.024) and total years of education (p=.049) also revealed to have significant associations with No Close Friends. Subjects who were not married scored higher than those who were married or had a partner and there was a tendency for elevated scores as the years of education increased. In model 2 of Constricted Affect, gender contributed independently and accounted for an additional 1.9% variance in the score. As seen in No Close Friends, marital status (p = .025) was also found to have a significant effect on the Interpersonal Factor (model 2). Besides the No Close Friends subscale and the Interpersonal Factor, marital status was shown to be a significant predictor for several other SPQ domains (model 2), SPQ total score (p=.004), Ideas of Reference (p=.007), Odd Behavior (p<.001) and Suspiciousness (p=.048) subscales, Cognitive Perceptual (p=.006) and Disorganised (p=.013) factors. Subjects who were not married displayed more elevated scores than those who were married or had a partner in these domains. 4. Discussion Western studies of schizotypy have shown that elements of schizotypal personality differ between males and females; males typically demonstrate more negative traits and females more positive traits. In our sample of over 500 participants, Asian males scored higher than Asian females on all domains of SPQ (Table 2) and as with previous studies, the main gender difference was significantly related to more negative schizotypal personality traits (Miettunen & Jaaskelainen, 2010), namely No Close Friends and Constricted Affect (Table 3) (Badcock & Dragovic, 2006; Bora & Arabaci, 2009; Miller & Burns, 1995; Raine, 1992). However, in contrast to previous western studies which showed that females have generally higher levels of Reference Ideas and Odd Beliefs / Magical Thinking (Badcock & Dragovic, 2006; Bora & Arabaci, 2009; Raine 1992; Roth & Baribeau, 1997), we found no elevation in positive schizotypal traits in this sample of Asian females. The result of positive schizotypal traits was in line with Miettunen & Jaaskelainen’s (2010) findings that there were no gender differences in the positive schizotypal scales (Magical Ideation Scale and Perceptual Aberration Scale) developed by Chapman,
407
Chapman, and Raulin (1976). These conflicting results may be due to the use of different instruments and the influence of culture in the presentation of positive schizotypal traits in Asian populations (Chen, Hsiao, & Lin, 1997). Significantly, a link has been reported between potential genetic susceptibility to schizophrenia spectrum disorders and gender expressions of schizotypy. Ma et al. (2007) investigated the association of potential susceptibility genes, catechol-Omethyltransfeerase (COMT), praline dehydrogenase (PRODH), and brain-derived neurotropic factor (BDNF) for schizophrenia and schizotypal personality traits in a nonclinical Chinese population. They found that gender had significant effects on SPQ subscales of Odd/Eccentric Behavior and Constricted Affect, with males scoring higher on both subscales. Furthermore, the Val158Met (rs4680) variant contributed significantly to the scores of the Constricted Affect subscale, Disorganised Factor and total score of SPQ in males suggesting that this gene may be linked to some schizotypal traits, at least in Asian males. The possibility that the genetic predisposition to schizophrenia spectrum disorders is reflected in sex related differences in schizotypal personality (Ma et al., 2007) presents exciting possibilities but remains to be further explored. Other potential explanations, such as the role of female sex hormones - in particular estrogen, could also play a part in the expression of schizotypal personality. There is an association between lower estrogen levels and exacerbation of psychotic symptoms and women with schizophrenia display more psychotic symptoms during premenstrual (low estrogen) period and fewer symptoms during pregnancy (high estrogen period) suggesting that estrogen may be protective against the development of schizophrenia (Kulkarni et al., 2008; Leung & Chue, 2000; Seeman & Lang, 1990). Although in this study we did not examine genetic or endocrine markers of schizotypy, the results show that the expression of schizotypal traits appears to differ not only along gender lines but is also linked to psychosocial success. These expressions provide useful indications of abnormality and could be used in future comparisons based on variations in genotype or other biological markers. In line with Miller and Burns (1995) contention that gender differences ‘‘. . .may be related to a broader aspect of Interpersonal and Social deficits, rather than a positive/negative dichotomy’’ (p.660), other results point to important differences in the spectrum of schizotypy. Marital status and years of education were significantly associated with SPQ especially on the subscales of No Close Friends, Reference Ideas, Odd Behavior, Suspiciousness and the three main factors of SPQ: Interpersonal, Cognitive-Perceptual and Disorganised. Subjects who were unmarried presented higher scores in these domains as compared to those who were married or had a partner. This effect, which was more pronounced than gender on the Interpersonal Factor, suggests that there is a link between schizotypal personality and the inability to form intimate adult relationships. In other words, individuals who withdraw from intimate relationships may be deprived of the benefits of validating and screening their ideas and perceptions with others, and emotional support from others which might elevate the positive schizotypal traits (Chapman, Chapman, Kwapil, Eckblad, & Zinser, 1994). Inability to form or maintain a close relationship is a common feature of schizophrenia (Thara & Srinivasan, 1997) and stigma relating to mental illness, particularly in Chinese societies which emphasize family and relationship (Lee, Lee, Chiu, & Kleinman, 2005), causes sufferers to experience social impairment and discrimination (Corrigan, 1998). That reduced success in education is also associated with the inability to form relationships underlines the importance of psychosocial indicators within the spectrum of schizotypal personality. Previous studies such as Miettunen et al. (2010) observed that higher education was associated with reduced negative
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schizotypy on the Social Anhedonia and Physical Anhedonia scales with participants of lower education level scoring higher on both scales. Although Ma et al. (2007) found an inverse relationship between the years of education and the score in the No Close Friends subscale in Chinese participants and it is possible that certain domains of the SPQ scale are specific to or behave differently across cultures (Chen et al., 1997), the pattern observed in our sample is in line with studies of the schizophrenia spectrum that have shown clear evidence of educational problems long before the onset of the illness (Crow, Done, & Sacker, 1995). There are several limitations to the present study. The current study is cross-sectional and by nature does not allow observations of the stability of schizotypal traits in relation to psychosocial factors. Secondly, ethnic differences need to be considered when assessing the validity of the SPQ. Although the mean total SPQ score (12.07) in our sample was broadly consistent with Chinese studies conducted by Chen et al. (1997) and Ma et al. (2007) who obtained scores of 12.9 and 19.17, respectively, Chinese SPQ scores are generally lower than those of western studies (ranging 23.5 to 27.8) (Hall & Habbits, 1996; Raine, 1991; Stefanis et al., 2006; Wuthrich & Bates, 2005). Although gender differences are by their nature intra-ethnic, the possibility of race gender interaction could not be explored in this study. Thirdly, only SPQ was administered in this study which does not include items that measure other schizotypal personality features such as anhedonia. Thus various schizotypy scales such as the Physical Anhedonia Scale (PAS) and the Social Anhedonia Scale (SAS) (Chapman, Chapman & Raulin, 1976) should be considered in future studies. Finally, examination of both gender and psychosocial factors such as education, job success and community integration, possibly also within the extended families of those with high schizotypal traits, may provide further clarification of the essential divergences that mark those at risk of schizophrenia. Role of funding source This study was funded by National Research Foundation, Translational Clinical Research – Neuroscience, Singapore. Conflict of interest The authors declare that there are no conflicts of interest. Acknowledgments We thank all the participants and the staff for their support of this study. References Badcock, J. C., & Dragovic, M. (2006). Schizotypal personality in mature adults. Personality and Individual Differences, 40(1), 77–85. Bora, E., & Arabaci, L. B. (2009). Effect of age and gender on schizotypal personality traits in the normal population. Psychiatry and Clinical Neurosciences, 63(5), 663–669.
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Personality and Individual Differences journal homepage: www.elsevier.com/locate/paid
Gender differences in schizotypal personality in a Chinese population Meng En Guo a,⇑, Simon Lowes Collinson a,b, Mythily Subramaniam a, Siow Ann Chong a a b
Research Division, Institute of Mental Health/Woodbridge Hospital, 10 Buangkok View, Singapore 539747, Singapore Department of Psychology, Faculty of Arts and Social Sciences, National University of Singapore, Block AS54, #02-07, 9 Arts Link, Singapore 117570, Singapore
a r t i c l e
i n f o
Article history: Received 27 June 2010 Received in revised form 29 October 2010 Accepted 2 November 2010 Available online 23 November 2010 Keywords: Schizophrenia Schizotypal personality traits Schizotypy SPQ Gender
a b s t r a c t Studies that have examined schizotypal personality traits using self-reported measures have found gender differences in the expression and degree of schizotypy. Despite the reported presence of schizotypal traits in Asian populations, putative gender differences have been almost entirely derived from studies of Western populations. This study examined the gender effect of schizotypy in a broad sample of the Chinese population in Singapore using the Schizotypal Personality Questionnaire (SPQ). The questionnaire was administered to 538 (308 males and 230 females) subjects (age range of 21–55). As with previous studies, gender differences were related to the presence of negative schizotypal personality traits, namely No Close Friends and Constricted Affect. The spectrum of differences in schizotypy was also extended to the psychosocial sphere as marital status and years of education were significantly associated with several SPQ domains. The findings suggest that there are common elements in Asian and Caucasian populations and that psychosocial risk is an important correlate of schizotypy. The implications of gender differences in the aetiology of schizophrenia spectrum disorders are discussed. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Research examining the spectrum of schizotypal personality within general populations has increased rapidly in recent years (Raine, 2006). Because trait-like features are present in individuals with or without Schizotypal Personality Disorder who are at heightened genetic risk for schizophrenia, examining schizotypy within general populations provides a means to examine biological and cognitive markers of schizophrenia without the confounding effects of severe psychotic symptoms (Raine & Lencz, 1995). There is evidence to suggest gender differences in the expression of symptoms in schizophrenia and may be important in the aetiology of the disorder (Castle, Abel, Takei, & Murray, 1995; Castle & Murray, 1991; Leung & Chue, 2000). Men with schizophrenia have an earlier onset, tend to have more negative symptoms and poorer psychosocial functioning. Women, on the other hand, are characterized by greater affective and paranoid symptoms and fewer functioning deficits (Goldstein & Link, 1988; Leung & Chue, 2000). Gender differences are also found in relation to schizotypal personality. Miettunen and Jaaskelainen’s (2010) meta-analysis on the Wisconsin Schizotypy Scales found that males are characterized by
⇑ Corresponding author. Tel.: +65 63893611. E-mail address: [email protected] (M.E. Guo). 0191-8869/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.paid.2010.11.005
higher scores on ‘negative’ schizotypal personality traits of social isolation with Physical Anhedonia and Social Anhedonia and in previous single studies on Schizotypal Personality Questionnaire (SPQ), males are found to score higher on No Close Friends and Constricted Affect (Badcock & Dragovic, 2006; Bora & Arabaci, 2009; Ma et al., 2007; Miller & Burns, 1995; Raine,1992), whilst several SPQ studies suggest that women are higher on ‘positive’ schizotypal personality traits - having higher rates of Ideas of Reference and Odd Beliefs/Magical Thinking (Badcock & Dragovic, 2006; Bora & Arabaci, 2009; Raine,1992; Roth & Baribeau, 1997). In contrast, conflicting findings have been reported by Roth and Baribeau (1997) and Ma et al. (2007) with male subjects reporting elevated rates of ‘positive’ schizotypal personality traits of eccentric/odd behavior, and Miller and Burns (1995) also did not find higher rates of ‘positive’ schizotypal personality traits in female subjects, whereas Miettunen & Jaaskelainen’s (2010) meta-analysis suggests there may be no difference between males and females in positive symptoms. In order to establish the validity of the Schizotypal Personality Questionnaire (SPQ) on Singapore Asian populations and further examine the gender effect of schizotypy in Asian subjects, we examined SPQ in a broad sample of the Chinese population of Singapore. As there are conflicting findings regarding the rates of negative and positive symptoms between males and female and based on the findings of several SPQ studies, the hypothesis of this study is that Asian men would score higher on ‘negative’ schizotypal personality traits and women would score higher on ‘positive’ schizotypal personality traits.
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2. Methods 2.1. Subjects Singapore is an island state in Southeast Asia with a multi-racial population of about 4.5 million. Those of Chinese descent (75.2%) constitute the majority of the population, follow by the Malays (13.6%), Indians (8.8%) and Eurasians and other groups (2.4%).This study was carried out in the country’s only state mental health treatment facility and it was a part of a larger study aimed at elucidating the genetic vulnerability or neurocognitive endophenotypes in schizophrenia. The study was approved by the relevant institutional ethics and review board – the National Healthcare Group Domain-Specific Review Boards (DSRB). All subjects were recruited from the community through advertisements. The subjects were of Chinese ethnicity aged between 21–55 years old, able to understand spoken English, completed at least 6 years of formal education and had no significant history of alcohol or drug abuse. Subjects were screened with the Structured Clinical Interview for DSM-IV Axis I disorders - Non-patient edition (SCID-I/NP; First, Spitzer, Gibbon, & Williams, 2007) to ensure that they did not have a history of psychiatric disorder or psychotic symptoms. The Schizotypal Personality Questionnaire (SPQ; Raine, 1991) was administered to all the subjects in individual sessions. All subjects gave written informed consent.
Social Anxiety, No Close Friends, Constricted Affect and Paranoid Ideation make up the Interpersonal Deficits factor. The third factor i.e. Disorganised deficits is composed of Odd Behavior and Speech. The scale was reported to have sound psychometric properties with high internal reliability (0.91), high test–retest reliability (0.82), convergent validity (0.59 to 0.81), discriminant validity (0.63) and criterion validity (0.68) (Raine, 1991).
2.3. Statistical analysis All statistical analyses were performed with SPSS 18.0 for Windows (SPSS, Chicago, USA). Statistical significance was set at p < .05. Descriptive statistics including mean and standard deviation (SD) for continuous variables, and frequency and percentages for categorical variables were computed to explore sociodemographics variables of the study sample. Independent sample t-tests were used to compare the means scores of all SPQ domains (SPQ total score, nine subscales and three factors) and continuous demographic variables between the males and females. Chi-square tests were used to test the categorical variables. Separate hierarchical multiple regressions were conducted for each SPQ component. Demographic variables, age, smoking habit, marital status, living status, education level, total years of education and occupation status were entered as control covariates in model 1 and gender was entered into model 2. Cronbach’s alpha was also conducted to explore the internal consistency of the nine SPQ subscales.
2.2. Measures The SPQ is a 74-item self-rated scale to assess all nine traits of Schizotypal Personality Disorder (SPD) listed in the DSM-III-R. The SPQ comprises yes/no items and the total score ranges from 0 to 74. The nine subscales can be computed using the summation of corresponding items and the three main factors, Cognitive-Perceptual Dysfunction, Interpersonal deficits and Disorganised deficits as outlined in the DSM, can be computed using summation of the corresponding subscales scores. Cognitive-Perceptual Deficits factor is the summation of Ideas of reference, Odd Beliefs / Magical Thinking, Unusual Perceptual Experiences and Paranoid Ideation.
3. Results 3.1. Descriptive statistics In all, 538 subjects were recruited for this study and the sample comprised 308 (57.2%) males and 230 (42.8%) females. The mean age of the subjects was 31.4 years (SD = 10.7), their mean years of education was 13.7 years (SD = 2.5), and most (N = 309, 58.1%) had high school, tertiary education, or technical education below university level. The majority of the subjects were not married
Table 1 Demographics characteristics comparison between males and females. Characteristics
Males (n = 308) Mean
Age (years) Education (years)
a b c
28.61 13.84
Females(n = 230) SD 9.22 2.11
Mean 35.13 13.46
Statistic
11.48 2.84
N
%
N
%
Education level Lowa Mediumb Highc
37 205 64
12.09 66.99 20.92
59 104 63
26.11 46.02 27.88
Marital status Married/had a partner Not married
63 245
20.45 79.55
102 128
44.30 55.65
Occupation status Employed Not employed/homemaker/retired Student
148 22 136
48.37 7.19 44.44
156 32 42
67.83 13.91 18.26
Smoking status Smoker Non smoker
48 260
15.60 84.42
15 215
6.50 93.50
Living status Self With others
10 298
3.25 96.75
4 225
1.75 98.25
Primary or secondary school level. High school, tertiary education, or technical education below university level. University level or above.
p
SD t = 7.07 t = 1.70
<.001 0.091
v2 = 26.64
<.001
v2 = 35.35
<.001
v2 = 41.77
<.001
v2 = 10.46
.001
v2 = 1.16
.281
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Table 2 Schizotypal personality traits comparison between males and females. Variable
Males (n = 308)
SPQ total score Ideas of Reference Excessive Social Anxiety Odd Beliefs/Magical Thinking Unusual Perceptual Experiences Odd Behavior No Close Friends Odd Speech Constricted Affect Suspiciousness/Paranoid Cognitive-Perceptual Factor Interpersonal Factor Disorganised Factor
Females (n = 230)
a
Mean
SD
a
Mean
SD
.88 .87 .87 .88 .88 .87 .87 .87 .87 .87 .85 .85 .86
13.11 1.76 2.08 1.23 0.51 0.64 1.83 2.17 1.42 1.48 4.98 6.81 2.81
10.11 1.87 1.97 1.34 0.85 1.21 2.03 2.06 1.71 1.56 4.30 5.98 2.86
.88 .87 .87 .87 .87 .87 .87 .87 .87 .87 .85 .85 .86
10.67 1.46 1.85 1.15 0.44 0.53 1.36 1.75 0.86 1.27 4.32 5.34 2.28
8.67 1.61 1.82 1.35 0.89 1.22 1.65 1.74 1.29 1.40 4.08 4.79 2.59
Statistic
p
t = 3.01 t = 1.96 t = 1.40 t = 0.73 t = 0.94 t = 1.00 t = 2.96 t = 2.57 t = 4.33 t = 1.61 t = 1.80 t = 3.16 t = 2.20
.003 .051 .162 .464 .350 .318 .003 .010 <.001 .108 .073 .002 .028
Table 3 Hierarchical regression coefficients for total score, the subscales of No Close Friends, Constricted Affect, Suspiciousness/Paranoid, Ideas of Reference, Odd Behavior and three factors of the Schizotypal Personality Questionnaire. Variable (regression 1)
Total score
DR 2 Step 1 Step 2 Age (years) Smoking status Living status Education (years) Educationa (medium level) Educationa (high level) Occupationb (employed) Occupationb (student) Marital status Gender Variable (regression 2)
0.045 0.005
Variable (regression 3)
Step 1 Step 2 Age (years) Smoking status Living status Education (years) Educationa (medium level) Educationa (high level) Occupationb (employed) Occupationb (student) Marital status Gender
Constricted Affect p
b
0.034 0.013 0.007 0.127 0.152 0.123 0.113 0.071 0.131 0.108
0.017 0.002
DR2
0.013 0.047 0.008 0.086 0.043 0.043 0.028 0.006 0.157 0.063
0.039 0.007
DR2
.904 .408 .242 .215 .159 .192 .236 .846 .025 .052
p
b
0.058 0.050 0.019 0.087 0.061 0.017 0.020 0.002 0.202 0.006
.399 .253 .675 .177 .436 .847 .788 .984 .000 .895
Disorganised Factor p
b
0.029 0.002 0.008 0.036 0.052 0.080 0.111 0.116 0.087 0.016 0.129 0.090
DR2
.845 .283 .854 .186 .583 .630 .699 .943 .007 .173
Cognitive Perceptual Factor p
b
.324 .188 .143 .219 .295 .478 .552 .630 .082 .001
0.042 0.000
.773 .293 .512 .710 .372 .338 .534 .633 .048 .327
Interpersonal Factor
0.067 0.058 0.065 0.079 0.082 0.063 0.043 0.040 0.100 0.148 Odd Behavior
p
b
0.030 0.003 0.020 0.047 0.030 0.024 0.071 0.086 0.046 0.040 0.116 0.046
p
b
.615 .765 .866 .049 .054 .165 .122 .392 .024 .020
Idea of Reference p
b
DR2 0.032 0.019
.775 .438 .276 .374 .270 .195 .762 .879 .004 .089
Suspiciousness/Paranoid
DR 2
DR2 0.033 0.010
0.019 0.034 0.048 0.057 0.087 0.114 0.022 0.013 0.168 0.078
DR 2 Step 1 Step 2 Age (years) Smoking status Living status Education (years) Educationa (medium level) Educationa (high level) Occupationb (employed) Occupationb (student) Marital status Gender
No Close Friends p
b
DR2
p
b
0.043 0.001 0.008 0.017 0.043 0.007 0.058 0.100 0.053 0.001 0.160 0.052
.909 .707 .335 .916 .463 .264 .470 .988 .006 .261
0.061 0.045 0.014 0.062 0.028 0.059 0.009 0.031 0.143 0.036
.369 .304 .761 .339 .721 .502 .900 .705 .013 .432
Note: Change in R2 values indicate the association significance test for change in R2 as each block of variables is entered into the model. Step 2 is controlled with age, smoking status, living status, education, occupation and marital status. Not reported in this table are the subscales of Odd Beliefs/Magical Thinking, Unusual Perceptual Experiences, Excessive Social Anxiety and Odd Speech which do not reveal any significant association. a Education (low level) as the reference group. b Occupation (unemployed/homemakers/retired) as the reference group.
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(N = 373, 69.3%), non-smokers (N = 475, 88.3%), employed (N = 304, 56.7%) and living with someone (N = 523, 97.4%). Table 1 presents the comparison of the demographics characteristics between the males and females. Males were more likely to be single, younger, smokers, students and with education above secondary level compared with the females. There were no significant differences in years of education and living status between males and females. The internal consistency of each SPQ subscale was high (Cronbach’s a range = 0.81–0.85) and independent sample t-tests revealed that males had higher scores than females in all the SPQ domains (Table 2). Males displayed significantly higher scores on the SPQ total score (p = .003), the negative subscales of No Close Friends (p = .003), Constricted Affect (p<.001) and the positive subscale of Odd Speech (p = .010). They also scored higher on the Interpersonal (p = .002) and Disorganised (p = .028) factors. No other significant gender differences were observed on other SPQ domains. 3.2. Hierarchical multiple regression analyses Table 3 illustrates the results of hierarchical multiple regression analyses and shows that gender differences remained significant in the following domains: No Close Friends (p = .020) and Constricted Affect (p = .001) with males scoring higher on both scales. However, the differences were not observed in the SPQ total score, Odd Speech, Disorganised and Interpersonal as reported in the univariate analyses. As reported in model 2 of No Close Friends, gender contributed an additional 1% variance in the score. Marital status (p=.024) and total years of education (p=.049) also revealed to have significant associations with No Close Friends. Subjects who were not married scored higher than those who were married or had a partner and there was a tendency for elevated scores as the years of education increased. In model 2 of Constricted Affect, gender contributed independently and accounted for an additional 1.9% variance in the score. As seen in No Close Friends, marital status (p = .025) was also found to have a significant effect on the Interpersonal Factor (model 2). Besides the No Close Friends subscale and the Interpersonal Factor, marital status was shown to be a significant predictor for several other SPQ domains (model 2), SPQ total score (p=.004), Ideas of Reference (p=.007), Odd Behavior (p<.001) and Suspiciousness (p=.048) subscales, Cognitive Perceptual (p=.006) and Disorganised (p=.013) factors. Subjects who were not married displayed more elevated scores than those who were married or had a partner in these domains. 4. Discussion Western studies of schizotypy have shown that elements of schizotypal personality differ between males and females; males typically demonstrate more negative traits and females more positive traits. In our sample of over 500 participants, Asian males scored higher than Asian females on all domains of SPQ (Table 2) and as with previous studies, the main gender difference was significantly related to more negative schizotypal personality traits (Miettunen & Jaaskelainen, 2010), namely No Close Friends and Constricted Affect (Table 3) (Badcock & Dragovic, 2006; Bora & Arabaci, 2009; Miller & Burns, 1995; Raine, 1992). However, in contrast to previous western studies which showed that females have generally higher levels of Reference Ideas and Odd Beliefs / Magical Thinking (Badcock & Dragovic, 2006; Bora & Arabaci, 2009; Raine 1992; Roth & Baribeau, 1997), we found no elevation in positive schizotypal traits in this sample of Asian females. The result of positive schizotypal traits was in line with Miettunen & Jaaskelainen’s (2010) findings that there were no gender differences in the positive schizotypal scales (Magical Ideation Scale and Perceptual Aberration Scale) developed by Chapman,
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Chapman, and Raulin (1976). These conflicting results may be due to the use of different instruments and the influence of culture in the presentation of positive schizotypal traits in Asian populations (Chen, Hsiao, & Lin, 1997). Significantly, a link has been reported between potential genetic susceptibility to schizophrenia spectrum disorders and gender expressions of schizotypy. Ma et al. (2007) investigated the association of potential susceptibility genes, catechol-Omethyltransfeerase (COMT), praline dehydrogenase (PRODH), and brain-derived neurotropic factor (BDNF) for schizophrenia and schizotypal personality traits in a nonclinical Chinese population. They found that gender had significant effects on SPQ subscales of Odd/Eccentric Behavior and Constricted Affect, with males scoring higher on both subscales. Furthermore, the Val158Met (rs4680) variant contributed significantly to the scores of the Constricted Affect subscale, Disorganised Factor and total score of SPQ in males suggesting that this gene may be linked to some schizotypal traits, at least in Asian males. The possibility that the genetic predisposition to schizophrenia spectrum disorders is reflected in sex related differences in schizotypal personality (Ma et al., 2007) presents exciting possibilities but remains to be further explored. Other potential explanations, such as the role of female sex hormones - in particular estrogen, could also play a part in the expression of schizotypal personality. There is an association between lower estrogen levels and exacerbation of psychotic symptoms and women with schizophrenia display more psychotic symptoms during premenstrual (low estrogen) period and fewer symptoms during pregnancy (high estrogen period) suggesting that estrogen may be protective against the development of schizophrenia (Kulkarni et al., 2008; Leung & Chue, 2000; Seeman & Lang, 1990). Although in this study we did not examine genetic or endocrine markers of schizotypy, the results show that the expression of schizotypal traits appears to differ not only along gender lines but is also linked to psychosocial success. These expressions provide useful indications of abnormality and could be used in future comparisons based on variations in genotype or other biological markers. In line with Miller and Burns (1995) contention that gender differences ‘‘. . .may be related to a broader aspect of Interpersonal and Social deficits, rather than a positive/negative dichotomy’’ (p.660), other results point to important differences in the spectrum of schizotypy. Marital status and years of education were significantly associated with SPQ especially on the subscales of No Close Friends, Reference Ideas, Odd Behavior, Suspiciousness and the three main factors of SPQ: Interpersonal, Cognitive-Perceptual and Disorganised. Subjects who were unmarried presented higher scores in these domains as compared to those who were married or had a partner. This effect, which was more pronounced than gender on the Interpersonal Factor, suggests that there is a link between schizotypal personality and the inability to form intimate adult relationships. In other words, individuals who withdraw from intimate relationships may be deprived of the benefits of validating and screening their ideas and perceptions with others, and emotional support from others which might elevate the positive schizotypal traits (Chapman, Chapman, Kwapil, Eckblad, & Zinser, 1994). Inability to form or maintain a close relationship is a common feature of schizophrenia (Thara & Srinivasan, 1997) and stigma relating to mental illness, particularly in Chinese societies which emphasize family and relationship (Lee, Lee, Chiu, & Kleinman, 2005), causes sufferers to experience social impairment and discrimination (Corrigan, 1998). That reduced success in education is also associated with the inability to form relationships underlines the importance of psychosocial indicators within the spectrum of schizotypal personality. Previous studies such as Miettunen et al. (2010) observed that higher education was associated with reduced negative
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schizotypy on the Social Anhedonia and Physical Anhedonia scales with participants of lower education level scoring higher on both scales. Although Ma et al. (2007) found an inverse relationship between the years of education and the score in the No Close Friends subscale in Chinese participants and it is possible that certain domains of the SPQ scale are specific to or behave differently across cultures (Chen et al., 1997), the pattern observed in our sample is in line with studies of the schizophrenia spectrum that have shown clear evidence of educational problems long before the onset of the illness (Crow, Done, & Sacker, 1995). There are several limitations to the present study. The current study is cross-sectional and by nature does not allow observations of the stability of schizotypal traits in relation to psychosocial factors. Secondly, ethnic differences need to be considered when assessing the validity of the SPQ. Although the mean total SPQ score (12.07) in our sample was broadly consistent with Chinese studies conducted by Chen et al. (1997) and Ma et al. (2007) who obtained scores of 12.9 and 19.17, respectively, Chinese SPQ scores are generally lower than those of western studies (ranging 23.5 to 27.8) (Hall & Habbits, 1996; Raine, 1991; Stefanis et al., 2006; Wuthrich & Bates, 2005). Although gender differences are by their nature intra-ethnic, the possibility of race gender interaction could not be explored in this study. Thirdly, only SPQ was administered in this study which does not include items that measure other schizotypal personality features such as anhedonia. Thus various schizotypy scales such as the Physical Anhedonia Scale (PAS) and the Social Anhedonia Scale (SAS) (Chapman, Chapman & Raulin, 1976) should be considered in future studies. Finally, examination of both gender and psychosocial factors such as education, job success and community integration, possibly also within the extended families of those with high schizotypal traits, may provide further clarification of the essential divergences that mark those at risk of schizophrenia. Role of funding source This study was funded by National Research Foundation, Translational Clinical Research – Neuroscience, Singapore. Conflict of interest The authors declare that there are no conflicts of interest. Acknowledgments We thank all the participants and the staff for their support of this study. References Badcock, J. C., & Dragovic, M. (2006). Schizotypal personality in mature adults. Personality and Individual Differences, 40(1), 77–85. Bora, E., & Arabaci, L. B. (2009). Effect of age and gender on schizotypal personality traits in the normal population. Psychiatry and Clinical Neurosciences, 63(5), 663–669.
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