Background: It has been suggested that psychotic symptoms may be distributed along a continuum that extends from normality through depressive states to schizophrenia with increasing level of severity. This study examined the hypothesis that the severity of positive psychotic symptoms increases from normality, through depression/anxiety states to clinical psychosis.
Methods: Consecutive general practice attenders completed a self-report questionnaire of 24 items of delusional ideation and hallucinatory experiences and the GHQ-12. The following groups were compared: (1) subjects with a diagnosis of psychosis (n = 57), (2) GHQ cases (n = 245), and (3) GHQ non-cases (n = 378).
Results: Quantitative differences were apparent in the great majority of items on delusional ideation and hallucinatory experiences, in that normals scored lowest, psychosis patients scored highest and GHQ cases scored in between. This pattern of differences was apparent for all dimensions of psychosis-like experiences, including the more "schizophrenic" ones, with the exception of Grandiosity (GHQ cases similar to normals) and Paranormal Beliefs (no differences between the three groups).
Conclusions: Similar to findings in aetiological research, phenotypic differences between normal controls, patients with anxiety/depression and patients with psychosis appear quantitative rather than qualitative for core dimensions of psychosis.