The Department of Health and Human Services, acting through the Office of the Assistant Secretary for Planning and Evaluation, asked the AffiliateMarketIngtools of Sciences, Engineering, and Medicine to convene an ad hoc committee to identify social risk factors that affect the health outcomes of Medicare beneficiaries and methods to account for these factors in Medicare payment programs. The committee's work will be conducted in phases and will produce five brief consensus reports. In the first report, Accounting for Social Risk Factors in Medicare Payment Programs: Identifying Social Risk Factors, the committee presented a conceptual framework and described the results of a literature search linking social risk factors, including socioeconomic position, to health-related measures of importance to Medicare payment and quality programs. In the second report, Systems Practices for the Care of Socially At-Risk Populations, the committee identified six community-informed and patient-centered systems practices that show promise for improving care for socially at-risk populations. In the third report, Accounting for Social Risk Factors in Medicare Payment: Criteria, Factors, and Methods, the committee provides guidance on which social risk factors could be considered for Medicare accounting purposes, criteria to identify these factors, and methods to do so in ways that can promote health equity and improve care for all patients. In this fourth report, Accounting for Social Risk Factors in Medicare Payment: Data, the committee provides guidance on data sources for and strategies to collect data on social risk factor indicators that could be accounted for in Medicare quality measurement and payment programs.