Mixed-footedness is a more relevant predictor of schizotypy than mixed-handedness Ulrich S. Tran a,n , Stefan Stieger a,b , Martin Voracek a a Department of Basic Psychological Research and Research Methods, School of Psychology, University of Vienna, Vienna, Austria b Research Methods, Assessment, and iScience, Department of Psychology, University of Konstanz, Germany article info Article history: Received 25 March 2014 Received in revised form 28 August 2014 Accepted 29 November 2014 Available online 10 December 2014 Keywords: Lateral preferences Latent class analysis Exploratory structural equation modeling Measurement equivalence abstract Mixed-handedness was reported indicative of schizotypy, relevant to psychosis and schizophrenia. However, studies suffered from validity threats and did not systematically investigate associations with footedness. Moreover, there is a dearth of studies in the general population and it is currently untested whether widely used self-report scales measure schizotypy in a comparable way in student and community samples. The present study used two large and independent community and student samples (total N42800) and utilized latent class analysis (LCA) for the classification of handedness and footedness. Psychometric properties and measurement equivalence of the Schizotypal Personality Questionnaire–Brief form (SPQ-B) in the two samples were also examined. We found that mixed- handedness ( o6% prevalence), but also much more common mixed-footedness (25% prevalence), was specifically and similarly associated with higher schizotypy in both samples, Cohen d ¼0.15–0.18. Findings indicate that schizotypal traits in conjunction with mixed lateral preferences are thus more prevalent in the overall population than previously assumed, and that footedness may be the more relevant predictor of schizotypy than handedness. Findings are further consistent with evidence on neurodevelopmental instability, but also epigenetic mechanisms involving the sex chromosomes, regarding possible common causes of both mixed-handedness and psychosis-relevant traits. & 2014 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Schizotypy is a multidimensional personality trait that refers to traits and symptoms similar to schizophrenia, but in a diminished form, and that reflects a liability for the development of schizophrenia- spectrum disorders (Kwapil et al., 2008; Lenzenweger, 2010). There is evidence for a dimensional continuum between schizotypy and schizophrenia (van Os et al., 2010; Giakoumaki, 2012; Linscott and van Os, 2013; Nelson et al., 2013), meaning that there is a phenomen- ological and temporal continuity between schizotypy and psychotic disorder (Linscott and van Os, 2013). Whereas the genetic bases of schizotypy and schizophrenia are still inconclusive (Crow, 2013; Nelson et al., 2013), the onset of psychotic syndromes is likely triggered by gene–environment interactions (van Os et al., 2010). One of the most reliable, and easily accessible, indicators for a risk for schizotypy (Somers et al., 2009) and schizophrenia (Sommer et al., 2001; Dragovic and Hammond, 2005) appears to be handedness, and in this regard specifically mixed-handedness. Handedness is indica- tive of language lateralization in the brain (Szaflarski et al., 2002, 2006) and may thus be considered an observable manifestation of cerebral lateralization. Ample evidence suggests abnormalities with regard to cerebral lateralization in schizophrenia, indicating that defi- cits in lateralization may play an important causal role (Crow, 2013). In a broader context, mixed-handedness was also reported a risk fac- tor for neurodevelopmental disorders in children (Rodriguez et al., 2010) and there is evidence that it is associated with prenatal expo- sure to maternal distress (Glover et al., 2004) and neurodevelop- mental instability (Rodriguez and Waldenström, 2008) that is also relevant for schizophrenia (Golembo-Smith et al., 2012). Even though there appears to be a robust association of mixed- handedness and schizotypy, extant studies faced some validity threats and suffer from possible shortcomings and bias. First, there is a 9:1 ratio of right- to non-right-handedness, requiring large sample sizes. Oversampling non-right-handers may result in dissimilarity of sam- pled populations and thus introduce additional bias. Second, classifica- tion of handedness often relies on arbitrary criteria and cutoffs, which may prohibit direct comparisons between studies (Beaton, 2008) or entail artificially heterogeneous results (Kelley, 2012). Third, footedness was reported a stronger predictor of language lateralization than hand- edness (e.g., Elias and Bryden, 1998), but is much less investigated. Exi- sting studies suggest that non-right-footedness plays a role for schizo- phrenia (Schiffman et al., 2005), but results for schizotypy are incon- sistent (Kelley and Coursey,1992; Nicholls et al., 2005; Asai et al., 2011). Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/psychres Psychiatry Research http://dx.doi.org/10.1016/j.psychres.2014.11.069 0165-1781/& 2014 Elsevier Ireland Ltd. All rights reserved. n Correspondence to: Department of Basic Psychological Research and Research Methods, School of Psychology, University of Vienna, Vienna; Postal address: Liebiggasse 5, A-1010 Vienna, Austria. Tel.: þ43 1 4277 47119; fax: þ43 1 4277 47192. E-mail address: ulrich.tran@univie.ac.at (U.S. Tran). Psychiatry Research 225 (2015) 446–451