Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Health Outcomes and Policy Research


Health Policy

Research Advisor

Shelley White-Means, PhD


Simonne S Nouer, PhD; Sam Li, PhD; Junling Wang, PhD; LaMarcus Wingate, Pharm.D., PhD


Diabetes Mellitus;Health Policy;Medication Adherence;Policy Analysis;Vulnerable Populations


Purpose. Low-income adults are disproportionately afflicted with diabetes and are more likely to suffer from advanced forms of diabetes related sequelae. Uninterrupted therapy on antidiabetic medications can postpone or prevent the damaging and costly complications associated with the progression of diabetes; however, many low-income individuals face significant barriers adhering to drug regimens. Medicaid, the primary source of health insurance among low-income people, mitigates access and cost barriers by providing access to health services and prescription drugs at a reduced cost. In 2014, Medicaid expansion, a provision of the Patient Protection and Affordable Care Act (PPACA), would have had the potential to significantly increase the number of Americans with Medicaid coverage. Yet only 27 states and Washington D.C. had expanded that year, following the Supreme Court’s decision that yielded Medicaid expansion noncompulsory for states. This schism amongst states conceived a unique opportunity in which researchers could compare Medicaid expansion effects on health outcomes. Since the implementation of Medicaid expansion, several studies have determined those states that adopted the expansion have had largely positive impacts on coverage, access to care and utilization, economic outcomes, as well as diminished disparities. There is a paucity of literature concerning the impact of PPACA on adherence to antidiabetic medication. Methods. This cross-sectional study analyzed pharmacy claims data collected by the Medical Expenditure Panel Survey (MEPS), a family of large-scale surveys that provides nationally representative estimates of health care use, expenditures, sources of payment, and health insurance coverage for the U.S. civilian noninstitutionalized population. MEPS respondents in years 2012/2013 (before expansion), and 2015/2016 (after expansion) were included in the study sample if they were between the ages of 19 and 64, reported income below 138% of the federal poverty level, and filled at least one antidiabetic medication during the study period. We utilized the difference-in-differences (D-I-D) statistical technique to estimate the causal effect of Medicaid expansion policy on adherence to antidiabetic medications among low-income adults who have been diagnosed with diabetes, characterizing treatment effect variation within specific marginalized subgroups. Adherence is determined in two ways: A multiple linear regression model estimated the effect of Medicaid expansion on mean adherence determined by the Medication Possession Ratio (MPR), and a multiple logistic regression model estimated the effect of Medicaid expansion on clinical adherence determined by MPR above 80%. Results. The sample included 1017 (weighted- 5,885,519) participants. The D-I-D estimate, which represents the change as a result of Medicaid expansion policy between treatment and control groups over time, was not significant in the multiple linear regression model (p=0.614). Likewise, the difference-in-differences estimate was not significant in the multiple logistic regression model (p=0.344). Among the studied subgroups, there was no significant association between Medicaid expansion and any measures of adherence studied; mean adherence or MPR greater than 80% (p>0.05). Conclusion. The findings suggest that Medicaid expansion policy alone could not overcome the barriers associated with medication adherence in this population. Policies are needed that intentionally address barriers associated with medication adherence among low-income adults with diabetes.

Declaration of Authorship

Declaration of Authorship is included in the supplemental files.