Geographic Variations in Health Care: Expanding Generalizability and Improving Relevance - A substantial amount of research over the past 50 years involving Medicare and other health insurance claims data has focused on evaluating variation in health care use and outcomes across geographic regions. For example, over the last quarter-century, the Dartmouth Atlas Project has focused on variation in Medicare feefor-service health care use for diagnostically defined cohorts of patients, often conditioning on future outcomes (e.g., death) to account for variation in health status. Numerous other claims studies have also used Medicare claims data to estimate comparative effectiveness of different treatments and procedures. Almost all of these types of research studies have used a nationwide measure of health care markets created at Dartmouth known as “Hospital Referral Regions (HRRs).” These regional markets, and the methodology underlying their delineation, have remained largely unchanged for nearly 30 years. In addition, because Medicare primarily covers individuals aged 65 and over, these regional measures—even at the time—are not representative of the whole population, leading to questions regarding the external validity of the published results especially given the tendency to equate such findings with the whole population. Motivated by the recent surge of interest in health and health care, a growing interest in cutting-edge statistical and machine learning methods, availability of newer and more extensive data on younger populations, and advances in network and geospatial analysis, this project proposes to revisit the methodology, definitions, and practical applications of regional and network measures of health care use and outcomes. These new approaches will avoid the potential fallacies of prior geographic measures by better capturing care patterns of populations of interest, and will facilitate geographic variations and comparative-effectiveness research with greater statistical power to detect effects of interest. Secondly, this project will develop new measures that quantify heterogeneity of geographic and other variations in use and spending across population strata, including heterogeneity indices. Thirdly, this project will evaluate the lack of representativeness of Medicare estimates and develop procedures to generalize results to other populations. Results of all analyses, including the algorithms for HRR delineation, will be used to modernize statistical and geographic approaches to characterizing health care access, use and outcomes. These will be widely disseminated to research and stakeholder communities, thus empowering health professionals and researchers to define analysis and administrative units pertaining to their specific health care systems and needs. This project will have a major impact on the research communities engaged in the evaluation of geographic variation in health care delivery and health outcomes.
