Hallucinations typically are associated with severe psychiatric illness but also are reported by individuals with no psychiatric history.

To examine the prevalence of hallucinations in White and ethnic minority samples using data from the Fourth National Survey of Ethnic Minorities.

Interviews of 5196 ethnic minority and 2867 White respondents were carried out. The respondents were screened for mental health problems and the Psychosis Screening Questionnaire asked about hallucinations. Those who screened positive underwent a validation interview using the Present State Examination.

Four per cent of the White sample endorsed a hallucination question. Hallucinations were 2.5-fold higher in the Caribbean sample and half as common in the South Asian sample. Of those who reported hallucinatory experiences, only 25% met the criteria for psychosis.

The results provide an estimate of the annual prevalence of hallucinations in the general population. The variation across ethnic groups suggests cultural differences in these experiences. Hallucinations are not invariably associated with psychosis.

The study of high-risk groups and the development of schizophrenia.

To investigate further schizotypy, measured by the Structured Interview for Schizotypy (SIS), and to examine relationships between schizotypal components, psychotic symptoms on the Present State Examination (PSE) and subsequent schizophrenia.

The SIS and PSE were administered on entry. Schizophrenia onsets were recorded during follow-up.

The SIS yielded four principal components labelled social withdrawal, psychotic symptoms, socio-emotional dysfunction and odd behaviour. On entry, these differentiated between controls, subjects at risk for schizophrenia with and without symptoms and patients with schizophrenia. Seven of 78 subjects at risk developed schizophrenia within 39 months. This was best predicted by combining the four SIS components.

Schizotypy is heterogeneous and may become psychosis, particularly if several of its components are present. As psychosis develops, odd behaviour gives way to psychotic symptoms and social function deteriorates.