Defense Date


Document Type


Degree Name

Doctor of Philosophy



First Advisor

Norman Carroll


INTRODUCTION: Medicare Part D provides prescription drug coverage to seniors through a benefit plan with a major deductible inserted in the middle. It is important to study the extent to which this structure affects seniors’ adherence to prescription medications. Therefore, this study had the following objectives: (1) To identify characteristics of beneficiaries reaching and not reaching the coverage gap, (2) To study the entry and exit times from the coverage gap, (3) To study the impact of a complete gap in coverage on beneficiaries’ adherence to prescription medications, (4) To study the impact of a partial gap in coverage on beneficiaries’ adherence to prescription medications METHODS: This was a retrospective quasi-experimental analysis with matched control groups using a nationally representative sample of Part D enrollees from 2008 Centers for Medicare and Medicaid (CMS) datasets. Adherence to each oral medication taken for one or more of the seven pre-defined therapeutic classes before and after reaching the coverage gap was measured using the Medication Possession Ratio (MPR). Appropriate statistical tests for significance were performed for each analysis RESULTS: A quarter of our sample (24.42%) reached the coverage gap in 2008. Most of the beneficiaries reaching the coverage gap did so by end of September. Those reaching the coverage gap and losing all coverage experienced significantly greater reductions in adherence (3% more for beta-blockers to 9% more for oral anti-diabetic agents), compared to those not reaching the coverage gap. A considerable proportion of beneficiaries stopped taking medications in both the groups and the proportion of beneficiaries considered adherent also dropped in both the groups during the coverage gap period. CONCLUSIONS: Medicare Part D beneficiaries face significant barriers to adherence and this is especially highlighted among those reaching the coverage gap. Interventions to improve adherence in this group should target all beneficiaries, especially those with several chronic conditions.


© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

August 2011