Do measures of schizotypal personality provide non-clinical analogues of schizophrenic symptomatology?

Abstract

This study tested the assumption that measures of schizotypal personality provide non-clinical analogues of the heterogeneous symptomatology found in the schizophrenic disorder. The Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE) was administered to schizophrenic patients and healthy controls, and measures of symptomatology from the Scale for the Assessment of Positive Symptoms (SAPS) and the Scale for the Assessment of Negative Symptoms (SANS) were assessed in the patient group. Schizophrenic patients scored significantly higher than controls on O-LIFE measures of positive, negative and disorganised schizotypy, while no difference in Impulsive Nonconformity was observed. In the patient group, SAPS positive symptomatology was significantly correlated with O-LIFE positive schizotypy (Unusual Experiences) and Cognitive Disorganisation. However, there was no significant relationship between SAPS/SANS disorganisation and O-LIFE Cognitive Disorganisation, or between the SANS negative factor score and O-LIFE Introvertive Anhedonia. The results suggest that the O-LIFE is a valid tool for assessing schizotypal personality in both schizophrenic patients and healthy controls. However, while the O-LIFE measure of positive schizotypy may correspond with SAPS/SANS positive schizophrenic symptomatology, the negative and disorganised subscales may not be analogous to their SAPS/SANS counterparts. There is also evidence to question the acceptability of Impulsive Nonconformity as a true schizophrenia-like construct.

Introduction

Contemporary authors generally conceptualise schizophrenia and other psychopathological disorders as extreme forms of disease processes. The quasi-dimensional approach stems from the psychiatric perspective and focuses on illness; specifically, the degrees of expression of a disease (Rado, 1953, Meehl, 1966). The fully dimensional approach incorporates the quasi-dimensional view of continuity, but also extends the continuity to include the healthy personality, which provides the starting point for the model. Thus, advocates of this model propose that the dimension of schizotypy lies on a continuum that begins with normality and proceeds towards the schizophrenia spectrum disorders, with schizophrenia at the upper end (Claridge and Beech, 1995).

A growing body of evidence has emerged to support the fully dimensional (or continuum) model of schizophrenia. Individuals high in schizotypal personality exhibit a range of cognitive and executive deficits (Peters et al., 1994, Park et al., 1995, Tsakanikos and Claridge, 2005) which are also found in schizophrenic patients (Beech et al., 1989, Liddle and Morris, 1991, Park and Holzman, 1992). Furthermore, the heterogeneous positive, negative and disorganised symptom subtypes found in schizophrenia (Liddle, 1987, Arndt et al., 1991) are also found in schizotypal personality (Raine et al., 1991, Chen et al., 1997).

Some authors report the presence of four schizotypal characteristics; namely the traditional positive, negative and disorganised factors and a fourth factor known as Impulsive Nonconformity (ImpNon) (Mason et al., 1995, Vollema and van den Bosch, 1995). However, Pickering (2004) argues that ImpNon is not a true schizotypal factor because it does not reflect cognitions or behaviours found in schizophrenia. Rather, ImpNon is more reminiscent of the impulsive, antisocial, sensation-seeking (ImpASS) traits found in certain personality disorders, such as borderline, schizoid or antisocial personality disorders. High ImpNon scores are not found in the relatives of schizophrenic patients (Claridge et al., 1983) and high ImpNon scores in healthy individuals do not significantly predict increased risk of psychosis (Chapman et al., 1994).

As previously stated, research has shown that schizophrenic-like symptoms are present, in an attenuated form, in the general population. The complex and multi-dimensional nature of schizotypal personality is captured through the use of reliable and valid measures such as the Schizotypal Personality Questionnaire (SPQ) (Raine, 1991) and the Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE) (Mason et al., 1995). The SPQ is based on DSM-III-R criteria for schizotypal personality disorder, while the O-LIFE is derived from factor-analytic studies of non-clinical measures (Mason et al., 1995, Vollema and van den Bosch, 1995). Schizophrenic symptomatology is assessed using standard clinical measures such as the Scale for the Assessment of Positive Symptoms and Scale for the Assessment of Negative Symptoms (SAPS/SANS) (Andreasen, 1983, Andreasen, 1984) and the Positive and Negative Syndrome Scales (PANSS) (Kay et al., 1987).

Interestingly, there is a striking paucity of research examining schizotypal characteristics in schizophrenic patients. It is generally assumed that non-clinical schizotypal measures are assessing schizophrenia-like traits in healthy individuals, but this assumption does not appear to have been formally tested. The central aim of this study was to compare the scores of schizophrenic patients and healthy controls on the O-LIFE measures of schizotypal personality. If schizotypy is truly a dimensional construct, and non-clinical measures assess schizophrenia-like characteristics, then the difference in schizotypy scores should be quantitative (i.e. higher in patients than controls) rather than qualitative. Another aim was to assess the relationship between SAPS/SANS symptomatology and O-LIFE schizotypal characteristics in schizophrenic patients.

It was hypothesised that the patients would score significantly higher than controls on the three traditional measures of schizotypy (positive, negative and disorganised). However, based on Pickering's (2004) assertion, it was expected that there would be no significant difference in Impulsive Nonconformity scores between the patients and controls. It was also expected that there would be significant positive relationships between scores on the SAPS/SANS and O-LIFE positive, negative and disorganisation scales in the patient group.

Finally, a measure of fluid IQ was included to rule out the possibility that any differences in symptomatology between patients and controls could be due to a cognitive artefact. Tests of fluid IQ are believed to assess a globally integrated (prefrontally mediated) cognitive function (Duncan, 1993, Duncan, 1995), and therefore an examination of this seemed particularly relevant for the current purposes. A more extensive battery of IQ tests was not possible in the time available as the patients were also tested on a battery of executive function tasks; a manuscript reporting the relationships between symptoms and performance on the executive function tests is currently in preparation.