Physician Markets and Patient Health

Although prior research has shown that physician market concentration leads to price increases for physician services, we consider whether the patients in concentrated areas pay for better care. Using medical claims for 5% Sample of Medicare FFS beneficiaries, we document the relationship between horizontal concentration on health care outcomes using both cross-sectional relationships, and changes over time linked to documented horizontal mergers in physicians markets. We measure the timing of complications from hypertension, diabetes and other chronic conditions; and associate this timing with horizontal concentration constructed from the Medicare data, as well as physician mailing lists. We also measure the effects of increases in concentration due to group acquisition using as a hand-curated list of mergers of physician groups.