Assessing the Importance of Factors Associated with Cost-Related Nonadherence to Medication for Older US Medicare Beneficiaries

Background: Prescription drug costs have been rising rapidly in the USA, contributing to the persistent problem of cost-related medication nonadherence (CRN) among older Medicare beneficiaries. Given the importance of CRN and the negative outcomes associated with it, it is important to examine the factors that affect CRN. This study aims to estimate the factors influencing CRN among older Medicare beneficiaries and to rank their relative contribution in explaining CRN. Methods: We used a 2015 Medicare Current Beneficiary Survey linked to Medicare claims data to identify older Medicare beneficiaries aged 65 years and over. Multivariate logistic regression was performed to identify factors associated with CRN. Factors included in the regression analyses were based on a conceptual framework adapted from Piette et al., including main effects (financial factors and regimen complexity) and contextual factors (sociodemographic, lifestyle and health factors). Dominance analysis was conducted to determine their relative importance in predicting CRN. Results: Our study sample included 4427 older Medicare beneficiaries, 13.43% of whom reported CRN. For main effects, drug coverage and regimen complexity were significantly associated with CRN. Compared to beneficiaries with public coverage, those with private drug coverage were less likely to report CRN while those without drug coverage were more likely to report CRN. Having more than two monthly prescriptions was also associated with higher CRN. Significant contextual factors included age, activities of daily living limitations, perceived health status, cancer, rheumatoid arthritis, non-rheumatoid arthritis, depression, and lung disease. Dominance analysis showed drug coverage was the most influential factor in explaining CRN, after which age, ADL limitations, and depression ranked in sequence. Conclusions: These findings can help policy makers understand the relative importance of factors affecting CRN and identify the most important areas for intervention to improve CRN.