The relationship between supply and hospitalization rates for mental illness and substance use disorders.

This study investigated the extent to which mental illness and substance use hospitalization rates were related to the supply of psychiatric treatment services. Supply variables, notably the per capita rate of psychiatrists, primary care physicians, and specialty units, were strongly related to mental illness and substance use hospitalization rates to acute care hospitals across 114 small geographic areas in Iowa. The supply of outpatient services was not related to hospitalization rates. The need to study the reliability of patient assessment processes, refine guidelines and admissions criteria, and understand the contributions of supply variables to hospitalization rates are indicated by these results. A conceptual model is offered within which the dynamic cycle from patient functioning to service delivery may be framed.