Schizophrenia Epidemiology

Incidence and prevalence

Good population-based incidence figures for child and adolescent onset schizophrenia are notably lacking. What data do exist describe broader categories of psychosis, with diagnoses made without the benefit of standardized assessments.

Gillberg et al. (1986) calculated age-specific prevalence for all psychoses (including schizophrenia, schizophreniform, affective psychosis, atypical psychosis and drug psychoses) in the age range 13 - 18 years using case-register data from Goteborg, Sweden.

Of the cases, 41% had a diagnosis of schizophrenia. At age 13 years, the prevalence for all psychoses was 0.9/10 000, showing a steady increase during adolescence and reaching a prevalence of 17.6/10 000 at age 18 years.

Sex ratio

Males are over-represented in many clinical studies of childhood onset schizophrenia (Russell et al. 1989; Green et al. 1992; Russell 1994; Spencer & Campbell 1994). However, other studies of predominantly adolescent onset schizophrenia have described an equal sex ratio (Gordon et al. 1994; Werry et al. 1994; Hollis 2000). The interpretation of these studies is complicated by the possibility of referral biases to clinical centres.

In an epidemiological study of first admissions for schizophrenia and paranoia in children and adolescents there was an equal sex ratio for patients under the age of 15 (Galdos et al. 1993; Lewine 1994). The finding of an equal sex distribution with adolescent onset is intriguing as it differs from the consistent male predominance (ratio 2:1) reported in incident samples of early adult onset schizophrenia (Castle & Murray 1991).

Clearly, future studies require population-based incident samples free from potential referral biases.

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