Selection experiences in Medicare HMOs: pre-enrollment expenditures

Area of Science:

• Health Economics
• Medicare Policy
• Healthcare Management

Background:

• Medicare beneficiaries are increasingly enrolling in Health Maintenance Organizations (HMOs).
• Understanding selection bias in Medicare HMO enrollment is crucial for policy and financial solvency.
• Previous research has not fully explored the nuances of selection bias across different enrollment durations and market conditions.

Purpose of the Study:

• To determine if Medicare beneficiaries enrolling in HMOs exhibit lower expenditures in the year prior to enrollment compared to continuous fee-for-service (FFS) beneficiaries.
• To investigate whether Medicare HMO enrollment bias is affected by market penetration and market-share growth rates.
• To analyze selection bias among short-term HMO enrollees.

Main Methods:

• Analysis of Medicare beneficiary data from 1993 and 1994.
• Comparison of expenditures between HMO enrollees and continuous FFS beneficiaries.
• Statistical testing for biased selection and its sensitivity to market characteristics.

Main Results:

• Favorable selection was observed for Medicare HMO enrollment, with lower prior expenditures.
• The degree of favorable selection decreased as HMO market share increased, but did not vanish.
• Unfavorable selection was found among short-term HMO enrollees.
• Selection bias was not significantly sensitive to HMO market penetration or growth rates.

Conclusions:

• Enrollment in Medicare HMOs is associated with favorable selection, particularly for longer-term enrollees.
• Market characteristics like penetration and growth do not fully explain variations in selection bias.
• Policy implications include the need to monitor selection effects and their impact on Medicare's financial stability.