Purpose: To examine the psychometric properties and validity of the 8-item Osteoporosis-Specific Morisky Medication Adherence Scale (OS-MMAS-8) in postmenopausal women prescribed bisphosphonates (BPs) for at least 15 months.
Methods: A random sample of women aged ≥55 years with osteoporosis prescribed daily or weekly BPs was identified. Pharmacy fill data were extracted to calculate the medication possession ratio (MPR). Eligible women were stratified by low (<0.50), medium (0.50-0.79), or high (≥0.80) MPR, with the a priori goal of recruiting 133 participants in each group. OS-MMAS-8 scores can range from 0 to 8 and were categorized as low (<6), medium (6 to <8), and high (8) adherence. Internal consistency reliability (Cronbach's alpha), test-retest reliability [intraclass correlation coefficients (ICCs)] and convergent validity (correlating OS-MMAS-8 with MPR and other self-reported measures) were assessed.
Results: A total of 400 women out of 449 respondents reported that they were still taking their BPs at the time of the survey and completed OS-MMAS-8. Overall, 38.5, 34.3, and 27.3% of participants had low, medium, and high OS-MMAS-8 scores, respectively. The mean (SD) MPRs according to OS-MMAS-8 scores (<6, 6 to <8 and 8) were 56.9 (22.6), 69.0 (24.9), and 76.7 (26.4), respectively. The correlation between OS-MMAS-8 and MPR was 0.36; p < 0.0001. Cronbach's alpha was 0.74, and the ICC was 0.83 (95% CI 0.76-0.88).
Conclusions: OS-MMAS-8 has acceptable psychometric properties for assessing medication adherence in postmenopausal women prescribed therapy for osteoporosis. Additional studies are needed to investigate the psychometric properties of OS-MMAS-8 in other settings and populations.