Life table analysis of membership in an HMO retention

The retention patterns of the Kaiser Foundation Health Plan (Oregon Region) were studied over a six-year period using a life table analysis. A 5% random sample, consisting of subscriber units that were enrolled at the initiation of the study of subsequently joined during the six-year period, were followed with respect to enrollment retention. The analysis presented here focuses on the 2,112 subscribers enrolled during the 1967-1970 period. These subscribers were characterized by the year they joined the plan and by their age and sex. The analyses showed that age of the subscriber and length of time on the plan consistently affected the probability of continued enrollment. The sex of the subscriber and the initial year of enrollment showed only a slight differential affect. A general pattern of high attrition in the first year, but rapid slackening thereafter, existed in all subgroup specific analyses. The utility of the analyses and the impact of the effect of differential membership retention on the plan are discussed.