A latent class analysis of psychosis-like experiences in the New Zealand Mental Health Survey

Objective:  To describe the underlying structure of psychosis-like experiences in the New Zealand Mental Health Survey.

Method:  A nationwide survey of household residents aged 16+ years was undertaken (n = 7435), using the Composite International Diagnostic Interview (3.0), including a six question lifetime screener for psychosis. Participants were grouped in three ways: by the number of 'symptoms' (occurring when not dreaming, half-asleep or under the influences of drugs) and by latent classes derived from binary responses (no/yes) or ordinal responses (never/sub-threshold/few times/many times).

Results:  Psychosis-like events were not uncommon (7.3%; 95% CIs 6.5-8.1), particularly experiences of visual (5.3%; 95% CIs 4.7-6.0) or auditory hallucinations (2.8%; 95% CIs 2.3-3.3). Both latent class analyses indicated a 'normal' class, a 'hallucinatory class' and a 'psychotic' class. The lifetime probability of anxiety, mood or substance disorders and the lifetime probability of seeking help for mental health problems increased from 'normal' to 'hallucinatory' to 'psychotic' classes and with the 'symptom' count.

Conclusion:  The presence of sub-threshold events and variation in the number of times a 'symptom' is experienced suggest a psychosis continuum. However, the latent classes labelled 'hallucinatory' and 'psychotic' differ markedly in symptomatology, which suggests some form of discrete clustering.