To assess the validity of self-report measures of diabetes medication adherence and evaluate the effect of depression on the validity of these reports.RESEARCH DESIGN AND METHODS
Adults with type 2 diabetes, treated with oral medications, completed a set of medication adherence self-reports that varied response scales and time frames, were administered structured clinical interviews for depression, and provided blood samples for HbA1c as part of a screening for an intervention study. A subsample of participants with HbA1c ≥7.0% and clinically significant depression received Medication Event Monitoring System (MEMS) bottle caps to record adherence. Analyses examined relationships between adherence measures and HbA1c and, in the subsample, MEMS. Moderated linear regression evaluated whether depression severity modified relationships with HbA1c.RESULTS
Participant (n = 170, 57% men, 81% white, mean HbA1c 8.3% [SD, 1.7]) adherence self-reports were significantly (r = −0.18 to −0.28; P < 0.03) associated with lower HbA1c. In the subsample (n = 88), all self-reports were significantly (r = 0.35 to 0.55; P ≤ 0.001) associated with MEMS-measured adherence. Depression significantly moderated the relationship between three of six self-reports and HbA1c; at high levels of depression, associations with HbA1c became nonsignificant.CONCLUSIONS
Results support the validity of easily administered self-reports for diabetes medication adherence. One-month, percentage-based ratings of adherence had the strongest associations with MEMS and HbA1c; those requiring the report of missed doses had weaker associations. One-week self-ratings and measures that require respondents to record the number of missed doses appear to be vulnerable to bias from depression severity.