Cases were ascertained from in-patient and out-patient psychiatric facilities in Ireland and Northern Ireland. Cases completed the same diagnostic instrument used in our prior family study, the Structured Clinical Interview for DSM III-R, Patient version with an expanded psychosis section27; DSM-III-R criteria were used for consistency with our family collection28. Detailed personal interviews and hospital record rating forms were completed for each proband. Subjects with a field diagnosis of schizophrenia or poor-outcome schizoaffective disorder were eligible if all four grandparents were born in Ireland or the UK. The ICCSS sample includes 1021 cases.
