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New SHADAC Brief Explores Methods for Adapting BRFSS Survey Income Measure to Align with FPG Thresholds
June 18, 2019:
The Centers for Disease Control and Prevention’s (CDC) Behavioral Risk Factor Surveillance System (BRFSS) survey can be a valuable data source for researchers seeking to evaluate the impact of health insurance coverage programs such as Medicaid on measures of health outcomes and health behaviors; yet the BRFSS’ income measure, which asks respondents to classify their income within one of eight possible categories, creates challenges when trying to define the relevant eligible populations.
A new brief from SHADAC evaluates common methods for better using categorical income measures, such as the one in the BRFSS, to calculate income as a percent of the federal poverty guidelines (FPG).
Evaluation and Methods
Three of the four methods start by assigning a continuous income value to the respondent based on the respondent’s reported income category, choosing either the lower bound of each category, the upper bound of each category, or the midpoint of each category. A fourth method utilizes the uniform distribution to randomly assign an income value within the reported category.
Employing data from the 2017 BRFSS, the brief presents the distribution of income as a percent of FPG produced by each method as well as the state-level poverty rates produced by each method. It then evaluates the accuracy of these methods using data from the 2018 Current Population Survey’s Annual Social and Economic Supplement (CPS-ASEC), which has both a categorical income measure and a continuous income measure. The brief compares the distribution of income as a percent of FPG produced by the CPS’s continuous income measure to the distributions of income produced by each method when applied to the CPS’s categorical income measure.
Conclusions
Evaluation results reveal substantial differences in the distribution of income as a percent of FPG produced by each of the methods. The brief shows that the lower bound method skews towards the lower part of the income distribution, that the uniform distribution and midpoint methods produce a more even distribution of income, and that the upper bound method skews towards the upper part of the income distribution. Comparing the distributions produced by these methods against the distribution from a continuous income measure, the brief concludes that the upper bound method is likely the most accurate method across the income distribution while also acknowledging that the best method for assigning continuous income remains partially dependent on which population(s) is most relevant to the researcher’s chosen outcomes for analysis.
SHADAC utilizes data from the BRFSS, CPS, and other federal surveys to produce measures on a range of topics including income inequality, social and economic determinants of health, health insurance coverage, cost of care, health behaviors and outcomes, access to and utilization of care, and public health. Visit our State Health Compare web tool to explore the data further.
Related Resources
FPG vs. FPL: What’s the Difference?
