Characteristics of early- and late-diagnosed schizophrenia: implications for first-episode studies.

First-episode studies of schizophrenia are being carried out in many places. However, previous work has suggested that only half of the patients with schizophrenia receive the diagnosis in the initial stages of the illness. We examined whether cases of early- and late-diagnosed schizophrenia differed with respect to key sociodemographic characteristics and indicators of service use that might bias first-episode studies. Individuals who (i) presented for the first time between 1983 and 1993 to psychiatric services in a defined urban area with a cumulative mental health case register; and (ii) received a diagnosis of schizophrenia at least once during their mental health career were identified (n = 186). This sample was divided into those who received the diagnosis of schizophrenia for the first time within the first year of service contact (early-diagnosed schizophrenia; EDS), and those who received it for the first time after the first year of service contact (late-diagnosed schizophrenia; LDS). The 10-year incidence of EDS and LDS were 10.4 and 7.0 per 100,000 person-years, respectively. EDS and LDS did not differ in their pattern of association with sex, single marital status and higher levels of neighbourhood socioeconomic deprivation. However, EDS was more incident in the higher age groups, and the level of service use was higher for EDS cases in the first years of contact with mental health services, with LDS cases gradually catching up and exceeding EDS service use later in the illness course. Although differences between EDS and LDS were few, studies of patients with schizophrenia in the 'first' episode are likely to be most representative if patients who receive the diagnosis for the first time after previous episodes of care for non-schizophrenic episodes are also included.