SELECTION BIAS IN HMOS AND PPOS - A REVIEW OF THE EVIDENCE

Early studies of selection bias found that group and staff model healt h maintenance organizations (HMOs) enjoyed favorable selection (i.e., attracted healthier enrollees) among the nonelderly population. This r eview concludes that all health plans which restrict an enrollee's cho ice of provider-that is, group, staff; and individual practice associa tion (IPA) HMOs and exclusive provider organizations (EPOs)-enjoy favo rable selection among both the nonelderly and elderly populations. Thi s suggests that the most important reason HMOs and EPOs experience fav orable selection is that individuals who consume large amounts of heal th resources often are unwilling to sever ties with their health care providers.