The multidimensionality of self-report schizotypy in a psychiatric population: An analysis using multidimensional Rasch models

There is increasing empirical evidence from factor analytical studies that schizotypy is composed of three dimensions, All studies into the multidimen sionality of schizotypy used common factor analysis of scales, either explo ratory or confirmatory. We argue that for research into the multidimensiona lity of schizotypy with dichotomous item responses on questionnaires las wi th the Schizotypal Personality Questionnaire [SPQ], Raine 1991) much can be learned using generalized multidimensional Rasch models (GMRMs), GMRMs req uire a priori postulated models of schizotypy, which can be tested in confi rmatory analyses. We hypothesized four competing models of schizotypy, base d on the literature and clinical impressions-two two-dimensional models and two three-dimensional models. We also hypothesized that items differ in th e degree they are indicative of a particular dimension of schizotypy. The s ample was 418 psychiatric inpatients and outpatients, with moderate levels of psychopathology, who filled in the SPQ, Both three-dimensional models yi elded a much better fit to the data than both two-dimensional models. Our r evised three-dimensional model, a revision of that by Raine et at. (1994) a nd Gruzelier (1996), yielded the best fit. It consisted of positive schizot ypy, disorganization, and negative schizotypy, The results strongly suggest that schizotypy, as measured with the SPQ, is a three-dimensional construc t.