All sites used
common diagnostic procedures so that joint analyses of the two
pedigree sets could be undertaken. Subjects came from families
with at least two biologically related first-degree relatives diagnosed
with the core illness. For schizophrenia sites, enrolled pedigrees
contained at least one relative pair in which one member
was diagnosed with schizophrenia and the other was diagnosed
with schizophrenia or schizoaffective depression. For the bipolar
disorder pedigrees, core diagnoses were bipolar illness in one relative
and bipolar or schizoaffective disorder (bipolar type) in another
biological first-degree relative (23). Subjects were interviewed
with the Diagnostic Interview for Genetic Studies (24),
and their clinical data were entered into the centralized database
established by the NIMH (SRA Technologies, Falls Church, Va.) as
of April 1996. The Diagnostic Interview for Genetic Studies directly
asks about the subject’s education and occupational functioning.
Occupational functioning is expressed numerically, reflecting
the level of managerial or professional responsibility, with
lower numbers reflecting positions with higher levels of responsibility
(according to a modification of the Hollingshead Four-Factor
Index of Social Position [25]).