The dimensional structure of short forms of the Wisconsin Schizotypy Scales
Introduction
Current research conceptualizes schizotypy as a multidimensional phenotype that encompasses clinical and subclinical manifestations of the schizophrenia spectrum (Lenzenweger, 2010, Kwapil and Barrantes-Vidal, 2014). Ample evidence supports significant overlap between schizotypy and schizophrenia across behavioral and neurobiological domains, suggesting that the identification of schizotypic individuals should facilitate the detection of etiological risk and protective factors for schizophrenia-spectrum disorders (for a review see Ettinger et al., 2014). It also allows for the examination of etiological factors relatively untainted by confounds accompanying full-blown schizophrenia, such as hospitalization, medication, and stigma. Since their development by the Chapmans and colleagues, the Wisconsin Schizotypy Scales (WSS, also known as the Chapman Scales of Psychosis Proneness)—including the Perceptual Aberration (Chapman et al., 1978), Magical Ideation (Eckblad and Chapman, 1983), Physical Anhedonia (Chapman et al., 1976), and Revised Social Anhedonia (Eckblad et al., 1982) Scales—have been widely employed in the study of schizotypy. Cross-sectional and longitudinal investigations provided evidence for the reliability and validity of the WSS (e.g., Gooding et al., 2005, Kwapil et al., 2008, Kwapil et al., 2013).
Schizotypy, and by extension schizophrenia, are conceptualized as multidimensional constructs (Raine et al., 1994, Vollema and van den Bosch, 1995, Stefanis et al., 2004), with positive and negative symptom dimensions the most consistently replicated factors. Using confirmatory factor analysis (CFA) with 6137 young adults, Kwapil et al. (2008) found evidence for a two-factor structure with positive and negative factors underlying the original WSS. In addition, they reported that, as hypothesized, the schizotypy dimensions were differentially associated with symptoms and impairment. Positive schizotypy was associated with psychotic-like experiences, substance abuse, mood disorders, and mental health treatment; negative schizotypy was associated with negative and schizoid symptoms and decreased likelihood of intimate relationships. Both dimensions were related to schizotypal and paranoid symptoms and poorer functioning. Kwapil et al. (2013) reported that both dimensions predicted schizophrenia-spectrum disorders using data from the 10-year follow-up study conducted by Chapman et al. (1994).
Despite the demonstrated validity of the WSS, the combined length of the scales (166 items) can be problematic; therefore, Winterstein et al. (2011) created 15-item short forms for each of the four WSS. They chose items based upon content analysis and psychometric properties using classical test theory, item response theory, and differential item functioning. Winterstein et al. (2011) reported good internal consistency for the short-form scales as well as preliminary evidence for validity. Gross et al. (2012) investigated the reliability and validity of the short-form WSS using interview ratings of psychotic-like and schizophrenia-spectrum symptoms and questionnaire measures of personality and social impairment. Despite the drastic reduction in items, the short scales demonstrated good reliability, correlated highly with the original scales, and exhibited hypothesized associations with measures of psychopathology, personality, and impairment. Fonseca-Pedrero et al. (2014) reported that the brief versions of the Perceptual Aberration and Magical Ideation Scales had good psychometric properties and loaded on a single underlying factor. However, they did not examine the properties of the anhedonia scales.
The present study extends the work of Winterstein et al. (2011), Fonseca-Pedrero et al. (2014), and Gross et al. (2012) by examining the factor structure underlying the short WSS in three large samples. This is the first study examining the dimensional structure of the short WSS and the validity of these dimensions. It was hypothesized that the two-factor structure reported by Kwapil et al. (2008) for the original scales will be replicated in the shortened scales. Assuming that the structure is supported, we hypothesized that the short-form dimensions would exhibit good temporal stability and comparable associations with measures of schizotypic symptoms, impairment, personality, and social functioning as reported in Kwapil et al. (2008).
Section snippets
Participants
WSS data were obtained from three large, independent samples of undergraduates. The first two samples completed the original WSS. We then derived the short WSS scores and dimensions from the original scales, allowing us to compare performance, factor structure, and the correlates of these factors between the original and short scales. The first sample included 6137 students (76% female) with a mean age of 19.4 (SD = 3.7). This sample was used by Kwapil et al. (2008) to examine the factor
Results
Descriptive statistics for the short WSS in the first two samples are reported in Gross et al. (2012) and descriptives for the third sample are reported in Table 1. These values were comparable across the three samples, and the short scales demonstrated good reliability and high correlations with their original scale counterparts.
Discussion
The construct of schizotypy affords a unique opportunity to investigate neurodevelopmental and psychosocial factors underlying schizophrenia. Further, it provides a rich model for conceptualizing psychosis as a dynamic continuum ranging from subclinical manifestations, to schizophrenia-spectrum personality disorders, to schizophrenia. Phenomelogical, genetic, cognitive, and neurobiological evidence for putative overlap between schizotypy and schizophrenia supports the dimensional
Role of funding source
Neus Barrantes-Vidal and Thomas R. Kwapil are supported by the Spanish Ministerio de Ciencia e Innovación (PSI2008-04178), Fundació La Marató de TV3 (091110), and the Generalitat de Catalunya (Suport als Grups de Recerca - 2009SGR672).
Contributors
Georgina M. Gross, MS, contributed to the design and analyses, and was lead author of the manuscript. Paul J. Silvia, PhD contributed to the analyses and writing of the manuscript. Neus Barrantes-Vidal, PhD, contributed to the writing of the manuscript and study design. Thomas R. Kwapil, PhD, designed the study and contributed to the data analyses and writing of the manuscript.
Conflict of interest
None of the authors had a conflict of interest.
Acknowledgments
We thank Martha Diaz and Leigh Dickerson for assistance with data collection, and Charlotte Chun and Sarah Sperry for the comments on drafts of this manuscript.
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