Family history information is available for 739 cases (72.4%). We defined positive family history (FH+) by report of 1 or more first-degree relatives with schizophrenia or unspecified functional psychosis. We restrict the definition to first-degree relatives because we expect greater reliability of reporting for immediate family members. Unspecified functional psychosis required positive report of one or more specific symptoms (delusions, hallucinations, incoherence, or bizarre behavior) not due to a mood disorder. Under this definition, there are 196 FH+ cases. We compare these to the most conservatively defined 478 FH− cases reporting no psychotic illness in either first or second degree relatives. This approach has ≥65% power to detect differences between the FH+ and FH− subsamples assuming the same parameters as in our case/control power calculation (MAF ≥20%, allelic OR ≥1.3 and alpha=0.05).
