Abstract
OBJECTIVES: To evaluate the reliability and factorial validity of the four-item Morisky Green Levine Medication Adherence Scale (MGLS) among Atherosclerosis Risk in Communities (ARIC) Study participants. METHODS: We used the cross-sectional visit 5 data from the ARIC Study to assess the measurement properties of the MGLS. We measured the internal consistency using Cronbach α (where α > 0.70 is considered reliable for group-level measurement), the response frequency, and the inter item correlation. Factor analysis of the MGLS and five other adherence items in the survey was conducted using a polychoric correlation matrix to examine the dimensionality that underlies the MGLS. A vanishing tetrad test was conducted to assess conformity with an effect indicator model. RESULTS: Among the ARIC visit 5 participants, 6,261 (96%) responded to the MGLS and other questions related to medication adherence in the survey (mean age 76 ± 5 years, 59% women). The Cronbach α for the MGLS was 0.47. The inter-item correlations ranged from 0.11 to 0.26. In the factor analysis of the medication adherence survey questions, a three-factor solution was used. One factor captured the extent of nonadherence, whereas other factors focused on the reasons for nonadherence. The MGLS items spread out across the factors that reflect the extent of as well as the reasons for nonadherence. The results of the vanishing tetrad test indicated that the MGLS consists of items other than effect indicators (P < 0.0001). CONCLUSIONS: The low reliability together with the factor analysis findings imply that the MGLS may reflect causes as well as the extent of medication adherence. The findings suggest that the MGLS, as presently used, lacks consistency in an elderly population.