Construct Validity and Factor Structure of Survey-based Assessment of Cost-related Medication Burden

Background: Millions of Americans are burdened by out-of-pocket prescription costs. Although many survey measures have been developed to assess this burden, the construct validity and the factor structure of these instruments have not been rigorously assessed. Objectives: To characterize the factor structure and the construct validity of items assessing cost-related medication burden. Methods: We applied exploratory factor and confirmatory factor analyses to the 2009 Medicare Current Beneficiary Survey, focusing on 10 items assessing cost-related mediation burden among a nationally representative sample of community-dwelling Medicare beneficiaries. The fit of competing models was compared using several indices. Results: The study population (N = 8777) was predominantly aged over 65 years (83.3%), female (54.4%), and white (84.3%). Two distinct factors were present for the medication cost-reduction strategies: (1) cost-related medication nonadherence and (2) drug-shopping behaviors, not directly impacting medication compliance. The two factors were moderately correlated (r = 0.55), highlighting the presence of a 2 distinct but related constructs for cost-related medication burden. An item assessing the use of mail or internet pharmacies did not load well on either factor and may not necessarily measure medication-related cost burden. An item assessing reduced spending on basic needs loaded strongly on the same factor with the cost-related medication nonadherence items, suggesting they together may represent extreme compensatory behaviors that may adversely affect health outcomes. Conclusions: Two distinct constructs were derived from these items examining cost-related medication burden. Although cost-related medication burden is often associated with nonadherence, drug-shopping behaviors that do not directly impact adherence are also important measure of this burden.