The effect of duration of membership in a prepaid group health plan on the utilization of services.

This study concerns the changes in the use of medical care services as the duration of membership in a prepaid group plan increases. For each of ten cohorts of members of the prepaid group practice in Columbia, Maryland, the use of provider visits (for both "well" care and "problem-oriented" care), of inpatient hospital services, and of prescribed drugs were determined, and time trends for each type of service were developed. The rate of total provider visits (TPV's per member) and the proportion of "well" care visits declined during the first year of membership and were followed by stabilization during the second year in the Plan. Because of large variations in hospital days, but only a small total number of hospital days, no association between hospital use and duration of membership could be shown. The rate of new prescriptions filled (NPF's) also decreased as length of time in the Plan increased.