An investigation into the relationship between Schizotypy and crime based reasoning in a non-clinical population

Research output: Other contributionpeer-review



In 2003, 90% of the prison population in England and Wales were categorised as having a mental illness (Birmingham, 2003). The male prison population contained a 1000 prisoners affected by Psychosis and nearly 2000 in need of immediate psychiatric treatment (Birmingham, 2004). Schizophrenia has been associated with an increased risk of criminality (Munkner, Haastrup, Joergensen & Kramp, 2009), high levels of reported aggression and violence during first time episode of psychosis (Harris et al., 2010).

Schizotypal psychopathological characteristics can be found on a continuum (Claridge & Brooks, 1984; Eysenck & Eysenck, 1975) whereby they vary in severity due to a continuous phenotype (Van Os et al., 2000) in contrast to the categorical model. Consequently, a sub-clinical category of psychopathological behaviour has been identified, referred to as Schizotypy (Claridge, 1998).


This thesis explores the reasoning abilities of non-clinical individuals screened for Schizotypal tendencies using the Peters Delusion Inventory (PDI, Peters et al., 2004). A series of specially designed unique crime based reasoning tasks were created to assess the potential differences, biases and errors in crime based reasoning when comparing high and low scoring individuals for Schizotypal tendencies.

In addition, participants completed a short interview or audio diary, to record their reflections about completing the task, as well as considering any emotional responses.


An innovative four-part self-referencing scale (me, family, friend & stranger) demonstrated that individuals typically made quicker decisions about themselves compared to making decisions about other people. However, reaction time data suggested that self-reference was unaffected by Schizotypy when engaged in crime based decision making (p > 0.05). Reaction times proved to be either unaffected by Schizotypy whilst completing crime based reasoning tasks or an insufficient measure of 3 the biases associated with Schizotypy. As an alternative, ‘data gathering’ measures provide a much more sensitive measure which helped to describe and detect the differences in Schizotypy, e.g. a significant main effect of reference level was found using ‘data garthering’ data (p < 0.05) and error score data (p< 0.05).

The modality in which the crime based reasoning tasks were presented impacted upon the biases associated with Schizotypy, as opposed to any differences being as a result of dual processing functions placing greater demands on cognitive functional processing.

The qualitative data provided a consistent and coherent account of metacognitive experience of reasoning whilst completing the tasks. The qualitative results have allowed a more coherent overview of the relationship and differences in experiences between high and low schizotypal scorers to emerge, based around the themes of emotion, justification and morality, and reasoning strategies (Wilkinson, Jones & Caulfield, 2011).


Each of the studies within this thesis contributes to a better understanding of the biases that impact upon crime based reasoning, as well as confirmation of a ‘jump to conclusions’ bias (Dudley & Over, 2003; Dudley & Over, 1997; Huq, Garety & Hemsley, 1988) occurring in those individuals who scored high for Schizotypal tendencies. Furthermore, high scoring individuals demonstrated a reduction in emotive responses to the reasoning task scenarios and in some cases reported seeking the fewest pieces of information upon which to base their decision (Wilkinson, Jones & Caulfield, 2011).

The qualitative methods developed for this research are particularly novel in the field of thinking and reasoning, and proved to be invaluable tools in helping shape the direction of the experimental work as well as providing better insight into the mechanisms involved in crime based decision making.
Original languageUndefined/Unknown
Media of outputThesis
PublisherBirmingham City University
Number of pages257
Publication statusPublished - 2011

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