The purpose of this dissertation is to better understand how cost-related medication nonadherence (CRN) has been impacted by the implementation of Medicare Part D. CRN can include not filling, stopping, or skipping doses of a prescription because of cost (Gellad, Haas, & Safran, 2007; Safran et al., 2005). Research demonstrating the impact of Medicare Part D on CRN is extremely limited. Studies have primarily investigated the effect of the benefit utilizing pharmaceutical claims and health care plan data (Chen et al., 2008; Joyce, Goldman, Vogt, Sun, & Jena, 2009; Lichtenberg & Sun, 2007; Schneeweiss et al., 2009; Yin et al., 2008) and do not differentiate beneficiaries by demographics or health status. While gender and racial disparities in noncompliance prior to Medicare Part D clearly existed (Gellad, et al., 2007; Heisler, Wagner, & Piette, 2005; Klein, Turvey, & Wallace, 2004; Piette, Heisler, & Wagner, 2004; Soumerai et al., 2006; Zivin, Ratliff, Heisler, Langa, & Piette, 2010), studies have not examined the prevalence of racial and gender disparities in CRN since the implementation of Medicare Part D.This dissertation is comprised of three discrete empirical manuscripts, with introductory and concluding essays. Cumulative advantage/disadvantage theory was used as a foundation for understanding the effectiveness of Medicare Part D. Longitudinal and cross-sectional analyses were conducted using data from the Health and Retirement Study (HRS) and the Prescription Drug Study (PDS), a subsample of the HRS, to examine racial and gender differences in CRN before and after the implementation of Medicare Part D and factors associated with the benefit that can potentially impact adherence. In particular, this study addressed the following questions: 1) To what extent do racial and gender disparities in CRN exist since the implementation of Medicare Part D? 2) Do the Medicare Part D Low-Income Subsidy (LIS), coverage gap, and restrictions directly and indirectly affect the relationship between race, gender, and CRN? and 3) How do factors associated with cumulative advantage/disadvantage theory, specifically socioeconomic and health status, directly and indirectly affect the relationship between race, gender, and CRN? The results suggest that older Black Americans and females are more likely to report CRN before and after Medicare Part D than older Whites and males. Applying for the LIS increases the risk of CRN and mediates gender differences. Racial disparities in CRN appear to be driven by having a Medicare Part D plan with a gap in coverage. Poorer health and lower annual income increases the likelihood of CRN, even after controlling for LIS status and Medicare Part D's cost containment provisions. Further, experiencing the coverage gap and restrictions have a direct effect on nonadherence due to cost. The findings provide important insights into Medicare Part D's effectiveness in eliminating racial and gender differentials in CRN. Implications for practice, policy, education, and future research are discussed.
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