Information on the race and ethnicity of individuals enrolling through the Health Insurance Marketplaces is critical for assessing past enrollment efforts, determining whether outreach campaigns should be modified or tailored moving forward, and identifying where to target outreach activities. However, approximately one-third of insurance applicants do not complete the race and Hispanic ethnicity questions on the Marketplace application.
The RAND Corporation's modified Bayesian Improved First Name Surname and Geocoding (BIFSG) method uses surnames, first names, and residential addresses to indirectly estimate race and ethnicity. We used 2015–2022 data from the Centers for Medicare and Medicaid Services Multidimensional Insurance Data Analytics System (MIDAS), which contains person-year level data for Marketplace enrollees. The surname and first name for each individual were used to estimate initial probabilities for each of the six mutually exclusive racial and ethnic groups: American Indian/Alaskan Native (AI/AN); Asian American, Native Hawaiian, and Pacific Islander (AANHPI); Black; Hispanic; Multiracial; and White. Geocoded address information was used to refine these estimations and generate final probabilities.
Self-reported race and ethnicity were missing for 32.5 percent of the 71,610,609 records across the eight years of MIDAS enrollment data (2015 through 2022). Using enrollees' records from other years to replace missing race and ethnicity reduced the level of missingness to 23.5 percent. Enrollees who self-reported race and ethnicity were more likely to be AANHPI than nonreporting enrollees for whom race and ethnicity were imputed (9.4 percent versus 6.7 percent) or White (59.5 percent versus 49.3 percent) and less likely to be Black (10.9 percent versus 15.7 percent) or Hispanic (17.9 percent versus 26.1 percent). When combining self-reported race and ethnicity data with the imputed race and ethnicity probabilities for enrollees who did not report their race and ethnicity, we estimated that 8.7 percent of Marketplace enrollees were AANHPI; 0.6 percent were AI/AN; 12.0 percent were Black; 19.8 percent were Hispanic; 1.8 percent were Multiracial; and 57.1 percent were White.
Based on conventional standards for C-statistics, the ability of the modified BIFSG to differentiate AANHPI, Black, Hispanic, and White enrollees from other groups was "excellent." It did not reach an "acceptable" level for AI/AN or Multiracial enrollees.1 Currently, we recommend that modified BIFSG-imputed race and ethnicity not be used to make inferences about AI/AN or Multiracial enrollees.