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Reduced Medicare Advantage Insurer Concentration Associated With Small Improvements In Market Outcomes, 2013-23
1Bowen Garrett (bgarrett@urban.org), Urban Institute, Washington, D.C.
Health Affairs (Project Hope)
|October 6, 2025
Summary
Medicare Advantage (MA) market concentration decreased but remains high. Lower concentration was linked to modest benefits like reduced costs for beneficiaries, but significant improvements require further decreases.
Area of Science:
- Health Economics
- Health Services Research
- Insurance Market Analysis
Background:
- Medicare Advantage (MA) enrollment has surged, offering beneficiaries numerous plan choices.
- Despite increased options, the MA market is dominated by a few large insurers, indicating high concentration.
Purpose of the Study:
- To analyze trends in MA insurer concentration from 2013-2023.
- To examine the relationship between insurer concentration and MA payments, premiums, rebates, and cost-sharing.
Main Methods:
- Utilized Medicare Advantage administrative data for the period 2013-2023.
- Assessed market concentration using the Herfindahl-Hirschman Index (HHI) and the number of insurers per county.
- Quantified the association between concentration changes and financial/plan characteristics.
Main Results:
- A notable decrease in MA insurer concentration was observed, though overall concentration remained high.
- Reduced concentration correlated with lower Medicare payments, decreased individual premiums, increased plan rebates, and less enrollee cost-sharing.
- The magnitude of these effects was quantitatively small.
Conclusions:
- While a trend toward less concentration in the MA market is evident, current levels still indicate high market concentration.
- Further reductions in MA insurer concentration are unlikely to yield substantial benefits for Medicare beneficiaries or the program unless concentration declines significantly below present levels.
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