Background: Low-value services account for $75 billion to $100 billion of U.S. health care spending. Primary care physicians (PCPs) have been conceptualized as potential gatekeepers for efforts to reduce low-value spending, but the share of low-value spending directly related to their services and referral decisions remains unclear .

Objective: To estimate the share of low-value spending on Medicare beneficiaries that is directly related to their attributed PCP’s services or referrals.

Methods and Findings: We analyzed Medicare Part B claims from a 20% random sample of beneficiaries enrolled between 2007 and 2014. The study population included beneficiaries who were …