Figure 1

Illustration of the mirror-image design. For a given drug, the number of admission days for a given patient was calculated for a period before the first recorded use of the drug (M₁, either 1 or 2 years), and a period of identical duration afterwards (M₂). These rates were then corrected for the overall admission rates, for all patients with schizophrenia, during the same M₁ and M₂ periods (see text). Patients were excluded who had no admissions falling in the M₁ period, thus selecting for patients with relatively severe disease. A central gap (C₁+C₂, each 30 days) was excluded to reduce the effects of regression to the mean and errors caused by small inaccuracies in the temporal recording of drugs.