Evidence for a gender-specific decline in the rate of schizophrenia in rural Ireland over a 50-year period.

The issue of whether the incidence rate of schizophrenia may have declined over recent decades has generated considerable controversy. This study sought to ascertain and interview all patients who satisfied contemporary diagnostic criteria for schizophrenia within a defined and unusually homogeneous region of rural Ireland having a total population of 25,178 people; morbid risk for schizophrenia was then examined by quinquennia of birth from 1920-24 to 1965-69. Morbid risk appeared essentially constant for persons born between 1920 and 1939 but fell by 37% for those born between 1940 and 1969, the fall being considerably more prominent in females (-56%) than in males (-19%). Attention is focused on sexual dimorphism in cerebral development and on temporal changes in endogenous or exogenous factors that influence the rate of occurrence of schizophrenia in females.