Evaluation of the Measurement Properties of Self-reported Medication Adherence Instruments Among People at Risk for Metabolic Syndrome: A Systematic Review.

PURPOSE: The purpose of this study was to present a systematic review of available published studies that evaluated the measurement properties of self-reported instruments assessing global medication adherence in adults at risk for metabolic syndrome.

METHODS: The authors searched PubMed, EMBASE, PsycINFO, and CINAHL in January 2015 for appropriate studies. The methodological quality (based on reliability, validity, responsiveness, and interpretability) of selected studies was assessed with the COSMIN checklist (Consensus-Based Standards for the Selection of Health Measurement Instruments).

RESULTS: Of the 44 studies reviewed, 32 used classical test theory, and 14 used self-reported medication adherence instruments. More than half the studies included patients with hypertension, followed by diabetes, dyslipidemia, and increased body mass index. Among the measurement properties, internal consistency, hypothesis testing, and structural validity were frequently assessed items, whereas only 1 study evaluated responsiveness, and none evaluated measurement error. The MMAS-8 (Morisky Medication Adherence Scale-8 items) and the Hill-Bone scale were the most frequently used instruments. They were found to be well validated, with strong evidence for internal consistency and strong positive evidence for reliability, structural validity, hypothesis testing, and criterion validity.

CONCLUSIONS: The MMAS-8 and Hill-Bone scale seem to be well-validated instruments for assessing medication adherence in adults at risk for metabolic syndrome. These findings may assist clinicians with selecting the appropriate instruments for assessing medication adherence in this population. However, further studies might be needed to define concepts to better understand the dimensions of each medication adherence instrument.