The Effect of Physician Group Mergers on the Health Outcomes of Medicare Beneficiaries

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# The Effect of Physician Group Mergers on the Health Outcomes of Medicare Beneficiaries
## Presenter: Brett Wendling
### Discussant: Ian McCarthy
### SHESG Annual Meeting, October 8, 2021

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# Changing physician landscape
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Data from AMA Physician Practice Benchmark Survey, 2012-2018

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# Changing physician landscape

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<img src="shesg-2021-wendling_files/figure-html/unnamed-chunk-3-1.png" style="display: block; margin: auto;" />
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Data from AMA Physician Practice Benchmark Survey, 2012-2018

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# Changing physician landscape

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<img src="shesg-2021-wendling_files/figure-html/unnamed-chunk-4-1.png" style="display: block; margin: auto;" />
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Data from AMA Physician Practice Benchmark Survey, 2012-2018

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# Changing Physician Landscape

Physicians are now:
- less likely to own their own practice
- more likely to be employed by a hospital or part of practice owned by hospital
- more likely to be part of a very large practice

**Relatively little research on practice structure**

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# What does this paper do?

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# In pictures

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**Practice at time** `\(t\)`
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**Practice at time** `\(t+1\)`
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at least half of physicians leave practice ("merger-to")
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at least 10% new physicians ("merger-from")
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# Identification and Estimation

- Outcomes: Mortality and progression of disease
- Identification: DD(ish)
- Estimation: OLS with indicators for different merger types and controls for patient characteristics

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# Some thoughts and questions

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# Capturing mergers in the data

- What happens if 50% of physicians leave a practice, and the practice subsequently (or concurrently) gains more than 10% of new physicians?
- What happens if physicians move practices more than once?

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# Are these mergers?

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**Sure**
- Bulk of a practice dissolves (50%)
- Existing practice expands by some meaningful amount (10%)
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**Not really**
- "merger-to" practices still exist
- very hard to distinguish horizontal vs vertical
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# If not mergers, what?

- Disruption in care
- Information transmission within practices
- Variations in practice styles due to peers

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# Identification

- Is this a DD? Didn't see an "ever treated" dummy or person fixed effect...
- Sample selection? How often does a person leave their physician after the physician changes practices?
- Block estimation predicts treatment using patient characteristics, but nothing about physician practices. What source of endogeneity is this intended to adjust for?
- Physicians may change practices due to their current patient profile or restrictions on how they can practice
- Are physician characteristics in the data?

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# Estimation

- What is the estimand of interest?
- Not an ATT without strong homogeneity assumptions (across people and over time)
- Staggered treatment, etc.

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# Final ideas

- Thinking about movement across practices...
- Could exploit variation in non-compete agreement enforcement (Hausman and Lavetti, 2019)