Enrollee mix, treatment intensity, and cost in competing indemnity and HMO plans.

Why do indemnity insurance plans cost substantially more per capita--77% more in our study--than HMOs? We answer this question using data from a large organization's insurance pool, covering 215,000 lives. We decompose cost differences for eight major medical conditions into four sources: demographics, incidence within demographic groups, treatment intensity, and prices per service. Greater incidence of disease in the indemnity plan (both from demographics themselves and within demographic groups) and higher prices each explain nearly 50% of the difference. Contrary to conventional wisdom, indemnity plans do not have greater treatment intensity.