Do Medicare HMOs cost shift?

We tested the hypothesis that health maintenance organizations (HMOs) increase their commercial premiums when Medicare pays less. Such a linkage would be taken as evidence of "cost shifting." Other studies have tested the cost-shifting hypothesis among health care providers, but this is the first to examine the HMO industry. Our data consisted of annual observations on all HMOs that operated in the United States between 1990 and 1995 and had a Medicare risk contract. A comparison group of HMOs that had no Medicare contract during that period also was analyzed. The main finding from this study is that HMOs have not shifted costs from Medicare to commercial premiums. This results supports the skeptical consensus that is developing toward the cost-shifting hypothesis. Additional findings include the negative effects of competition and for-profit status on HMOs' commercial premiums.