Using the MAX-NHANES Merged Data to Evaluate the Association of Obesity and Medicaid Costs

The MAX Medicaid policy issue brief series highlights the essential role MAX data can play in analyzing the Medicaid program. MAX is a set of annual, person-level data files on Medicaid eligibility, service utilization, and payments that are derived from state reporting of Medicaid eligibility and claims data into the Medicaid Statistical Information System (MSIS). MAX is an enhanced, researchfriendly version of MSIS that includes final adjudicated claims based on the date of service, and data that have undergone additional quality checks and corrections. CMS produces MAX specifically for research purposes. For more information about MAX, please visit: http://www. cms.gov/Research-Statistics-Data-and-Systems/Computer-Data-and-Systems/MedicaidDataSourcesGenInfo/ MAXGeneralInformation.html. The Medicaid Analytic eXtract (MAX) data set is derived from the state reporting of Medicaid eligibility and claims data and is designed to enable research on Medicaid enrollment, service utilization, and expenditures per calendar year at the enrollee level. The National Health and Nutrition Examination Survey (NHANES), a nationally representative survey of the U.S. noninstitutionalized population, collects measured heights and weights, the most accurate way to calculate weight status. This brief uses the 1999–2004 merged MAX-NHANES data to evaluate the association of Medicaid costs and obesity. The merging of these data sets was highly anticipated because each is considered the gold standard within its field. The results of the analysis demonstrate the hazard of using a small national survey (NHANES) with a state-based data system (MAX) to perform cost analyses, particularly when the range of realistic costs is large. Researchers should be aware of how their research decisions will affect the sample size and thus their ability to detect significant findings. With thoughtful consideration, the MAX-NHANES data have the potential to provide valuable insights for researchers and policymakers.