Robust Selection of Adherence Measures for Meta-Analysis

Fifteen studies reported multiple associations of beliefs related to different adherence measurements (details reported in Table 1). Where the choice was between adherence measures, the most objective measure was selected for the meta-analysis. Therefore, electronic monitoring of adherence [20] and prescription redemption data [16] were chosen over self-report. Where data was presented for both ‘on demand’ and prophylactic medications, data for the prophylactic medication data were chosen [21] (link), [22] , for consistency with medications prescribed for other long-term conditions. In studies where cross-sectional and longitudinal data were both available, longitudinal data was used within the analysis [21] (link), [23] (link)–[26] (link). Where one group provided cross-sectional data at multiple timepoints, the timepoint with the fewest missing data points was selected [27] (link). If the choice was between two self report measures of adherence, we used the more commonly used measure. Thus the Morisky Medication Adherence Scale (MMAS) was chosen over the Brief Medication Questionnaire [28] (link) and the ACTG adherence measure was used over the Walsh VAS scale [29] (link). Where patients within a sample were taking multiple medications and individual associations were provided for each medication [30] , [31] (link), the mean association was used within the meta-analysis but individual effect sizes are reported in Table 1 to facilitate comparison. Where data on two samples are reported within the same study [32] (link), [33] (link) we included both associations within the analysis.