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JAMA Guide to Statistics and Methods
December 10, 2014

Methods for Evaluating Changes in Health Care Policy: The Difference-in-Differences Approach

Author Affiliations
  • 1The Center for Healthcare Outcomes and Policy, University of Michigan, Ann Arbor
  • 2Institute for Healthcare Policy and Innovation, University of Michigan, Ann Arbor
  • 3Department of Surgery, School of Medicine, University of Michigan, Ann Arbor
  • 4Department of Health Policy & Management, School of Public Health, University of Michigan, Ann Arbor
JAMA. 2014;312(22):2401-2402. doi:10.1001/jama.2014.16153

Observational studies are commonly used to evaluate the changes in outcomes associated with health care policy implementation. An important limitation in using observational studies in this context is the need to control for background changes in outcomes that occur with time (eg, secular trends affecting outcomes). The difference-in-differences approach is increasingly applied to address this problem.1