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Abstract
Although dichotomously defined for clinical purposes, psychosis may exist as a continuous
phenotype in nature. A random sample of 7076 men and women aged 18-64years were interviewed
by trained lay interviewers with the Composite International Diagnostic Interview
(CIDI). Those with evidence of psychosis according to the CIDI were additionally interviewed
by psychiatrists. For the 17 CIDI core psychosis items, we compared a psychiatrist's
rating of hallucinations and/or delusions (Clinical Psychosis; sample prevalence 4.2%)
with three other possible positive CIDI ratings of the same items: (i) symptom present,
but not clinically relevant (NCR Symptom; sample prevalence 12.9%); (ii) symptom present,
but the result of drugs or somatic disorder (Secondary Symptom; sample prevalence
0.6%); (iii) symptom appears present, but there is a plausible explanation (Plausible
Symptom; sample prevalence 4.0%). Of the 1237 individuals with any type of positive
psychosis rating (sample prevalence 17.5%), only 26 (2.1%) had a DSM-III-R diagnosis
of non-affective psychosis. All the different types of psychosis ratings were strongly
associated with the presence of psychiatrist-rated Clinical Psychosis (NCR Symptom:
OR=3.4; 95% CI: 2.9-3.9; Secondary Symptom: OR=4.5; 95% CI: 2.7-7.7; Plausible Symptom:
OR=5.8; 95% CI: 4.7-7.1). Associations with lower age, single marital status, urban
dwelling, lower level of education, lower quality of life, depressive symptoms and
blunting of affect did not differ qualitatively as a function of type of rating of
the psychotic symptom, were similar in individuals with and without any CIDI lifetime
diagnosis, and closely resembled those previously reported for schizophrenia. Presence
of any rating of hallucinations was strongly associated with any rating of delusions
(OR=6.7; 95% CI: 5.6-8.1), regardless of presence of any CIDI lifetime diagnosis.
The observation by Strauss (1969. Hallucinations and delusions as points on continua
function. Arch. Gen. Psychiatry 21, 581-586) that dichotomously diagnosed psychotic
symptoms in clinical samples are, in fact, part of a continuum of experiences, may
also apply to the general population. The boundaries of the psychosis phenotype may
extend beyond the clinical concept of schizophrenia.