Objective: This study was undertaken to assess the twentieth-century literature on outcome in schizophrenia for historical trends that might be associated with changes in diagnostic and therapeutic practice and to test the hypothesis that both improved biological treatment and changes in diagnostic criteria have influenced outcome.

Method: Meta-analysis of the international literature on outcome in schizophrenia or dementia praecox from 1895 to 1992 identified 821 studies; 320 of these, with 51,800 subjects in 368 cohorts, met the inclusion criteria for the study.

Results: Only 40.2% of patients were considered improved after follow-ups averaging 5.6 years (range = 1-40). Outcome was significantly better when patients were diagnosed according to systems with broad criteria (46.5% were improved) or undefined criteria (41.0% were improved) rather than narrow criteria (27.3% were improved). The proportion of patients who improved increased significantly after mid-century (for 1956-1985 versus 1895-1955, 48.5% versus 35.4%), probably reflecting improved treatment as well as a broadened concept of schizophrenia. However, in the past decade, the average rate of favorable outcome has declined to 36.4%, perhaps reflecting the re-emergence of narrow diagnostic concepts.

Conclusions: Overall, less than half of patients diagnosed with schizophrenia have shown substantial clinical improvement after follow-up averaging nearly 6 years. Despite considerable gains in improvement rates after mid-century, there has been a decline since the 1970s. These historical changes probably reflect improved treatment, shifts in diagnostic criteria, and selection bias related to changes in health care.