Decomposing pharmaceutical cost growth in different types of health plans

Objective: To decompose pharmaceutical spending growth into price and quant ity components and to compare growth across different types of health plans Study Design: Retrospective analysis of pharmaceutical claims for active em ployees of a large national employer from 1996 to 1998, who were enrolled i n traditional fee-for-service plans, health maintenance organizations (HMOs ), and preferred provider organizations. Outcome Measures: Outcomes measures included total cost growth, price growt h, and quantity growth. Quantity growth was divided into growth in use of e xisting products and in use of newly introduced products. For existing prod ucts, quantity growth was further decomposed into growth in the number of p rescriptions and change in the mix of prescriptions. Results: During the study period, HMOs had the greatest cost growth. This d ifferential cost growth was largely attributable to changes in utilization as opposed to changes in prices, which were similar among types of health p lans. Introduction of new products contributed 15 to 20 percentage points t o cost growth in each setting. Differences in cost growth were largely attr ibuted to differences in the growth rate of spending on existing products. For existing products, the impact of increases in the number of prescriptio ns was much greater in the HMOs, while the impact of changes in the mix of prescriptions was only mildly greater in the HMOs. Conclusions: Pharmaceutical cost growth was largely attributable to changes in utilization as opposed to changes in prices. Changes in utilization pat terns were complex and differed across types of health plans.