IntroductionValid measurements of medication adherence are essential in clinical research. Numerous methods for measuring adherence exist, but electronic monitoring (EM) is currently considered the gold standard. The purpose of this study was to compare EM measurement to that of a smartphone application (app) to determine if the measures are comparable.MethodsThis was a secondary analysis of data from a randomized controlled trial of a behavioral economics-based telehealth intervention delivered by a smartphone app. Acute coronary syndrome (ACS) patients were enrolled from a hospital in the northeastern US and randomized to intervention or control arms. Daily medication adherence was monitored for 3 months after hospital discharge. Daily financial incentives were provided to individuals for photographing themselves taking their medication in the app. In this analysis, only those in the intervention arm who had both EM and app-based medication adherence data were examined. Differences in adherence rates between methods were calculated (EM - App) and plotted against the mean adherence of the two methods, per subject, in a Bland Altman Plot.ResultsOf the 44 participants in this sample 56% were male, 39% African American, and the average age was 59 (SD 10) years. The mean adherence rates were 78% (SD 27%) using EM and 92% (SD 17%) using the app. The mean (95% CI) difference between methods was -13.5% (-22.5%, -4.5%), with levels of agreement ranging from -71.8% (-87.5%, 56.1%) to 44.8% (29.1%, 60.4%). The negative coefficient of the mean difference in adherence rates between methods suggest that EM underestimated medication adherence compared to the app.ConclusionsThe two methods compared are not interchangeable as measures of medication adherence. These patients appear to have used the app more routinely than the EM device.