Research directions in psychiatric epidemiology.

A sufficient number of studies of geographically defined populations have now been done so as to make it clear that when all the various kinds of mental illnesses are lumped together, the total prevalence rates commonly amount to 20% or more. These findings imply major challenges to theory, policy, administration, and practice in the health field, and point to a need for vastly more information and understanding. This article sketches some of the directions such investigations might take.