The validity of Psychosis Proneness Scales as vulnerability indicators in recent-onset schizophrenia patients.

The Psychosis Proneness Scales developed by the Chapmans and colleagues [Chapman, J.P., Chapman, L.J., Kwapil, T.R. Scales for the measurement of schizotypy. In: Raine., A., Lencz, T., Mednick, S.A., (Eds.). Schizotypal Personality. New York: Cambridge University Press, 1995. pp. 79-109] are widely used to identify non-patient individuals who are hypothesized to possess heightened vulnerability to schizophrenia and related psychopathology. Yet surprisingly little is known about whether schizophrenia patients themselves show abnormalities on these scales across different clinical states, as would be expected for vulnerability indicators. Scores on four of the Psychosis Proneness Scales were evaluated at three assessment points over a 15-month period in healthy controls (n=54) and in recent-onset schizophrenia patients (n=72) who experienced symptom fluctuations across assessments. Patients showed steady elevations on the Physical Anhedonia Scale across time and clinical state, consistent with a stable vulnerability indicator. Patients had higher scores on the Perceptual Aberration and Magical Ideation Scales than controls throughout the follow-up period but scores also changed across clinical states, consistent with a mediating vulnerability indicator. Patients had higher scores on the Impulsive Non-Conformity Scale than controls only during a psychotic state, reflecting an episode indicator. The longitudinal characteristics of these scales in people who are actually diagnosed with schizophrenia provide key evidence for the validity of three commonly used psychometric indicators of vulnerability to psychosis.