Preliminary development of the Medication Nonpersistence Scale.

OBJECTIVES: To develop the Medication Nonpersistence Scale (MNPS)-a multi-item self-reported scale to measure medication persistence. SETTING: Six hundred seventy-five patients patronizing 3 separate independent community pharmacies in the southeastern United States participated in this research. PRACTICE INNOVATION: The MNPS, a self-reported measure, developed to provide an estimate of, and reasons for, medication nonpersistence. EVALUATION: Cross-sectional survey data were linked with retrospective prescription fill data obtained from 3 independent community pharmacies in the southeastern United States. The MNPS factor structure was studied by means of confirmatory factor analysis (CFA), and its scale reliability and convergent validity were evaluated with the use of the results of this analysis. Its concurrent validity was tested against a standardized days-to-discontinuation measure calculated over the past 12 months, and an attempt was made to arrive at an optimum cutoff point to identify patients who have been nonpersistent with their medications. RESULTS: The survey yielded 675 usable patients. The CFA confirmed a single-factor solution with good model fit (root mean square error of approximation = 0.06 [90% CI 0.05-0.07]; comparative fit index = 0.96). Moderate to strong evidence of scale reliability (Cronbach alpha = 0.75; construct reliability = 0.94; index of composite reliability developed for binary items = 0.91), convergent validity (standardized factor loadings >0.5 and statistically significant), and concurrent validity (unstandardized regression coefficient = -3.97; P = 0.03) was observed. Individuals who score 1 or higher on the MNPS were considered to be nonpersistent. CONCLUSION: The MNPS demonstrated good psychometric properties and offers a useful first step toward the self-reported measurement of medication persistence in clinical practice and research.

Development of the medication adherence estimation and differentiation scale (MEDS).

OBJECTIVES: To develop a self-reported measure for medication adherence and compare its ability to predict the proportion of days covered (PDC) with contemporary scales. METHODS: Retrospective prescription fill data from three community pharmacies in the Southeastern US were assessed to identify patients that were 18 years of age or older, and had received at least one medication for diabetes, hypertension, or dyslipidemia. A cross-sectional survey containing the Medication adherence Estimation and Differentiation Scale (MEDS) was administered among these pharmacy patrons. The MEDS assessed the extent and reasons for non-adherence. Survey responses were anonymously linked with retrospective prescription fill data. A total of 685 patients were sampled. The proportion of days covered (PDC) was used as the criterion measure. The Morisky, Green, and Levine Adherence Scale (1986 Morisky scale) and the Medication Adherence Reasons Scale (MAR-Scale) were used as comparators. RESULTS: The MEDS presented a five-factor solution-worries about side-effects, worries about addiction, worries about cost, lack of perceived need, and unintentional non-adherence (CFI = 0.97; RMSEA = 0.06; SRMR = 0.03; standardized factor loadings greater than 0.5, and statistically significant). The relationship between MEDS scores and PDC was statistically significant (unstandardized regression coefficient = -0.50, p < .01). The MEDS performed better than the 1986 Morisky scale (R2 = 0.02 vs 0.05, standardized regression coefficient = -0.13 vs -0.21) and the MAR-Scale (R2 = 0.02 vs 0.05, standardized regression coefficient = -0.12 vs -0.21) in predicting PDC. CONCLUSIONS: The MEDS demonstrated good psychometric properties and performed better than the comparator scales in the prediction of PDC.