Intervention IP-088: A randomized controlled trial of positive-affect intervention and medication adherence in hypertensive African Americans

The main outcome measures were medication adherence (assessed with electronic pill monitors) and within-patient change in BP from baseline to 12 months.

The secondary outcome was within-patient change in office BP from baseline to 12 months.

Based on the intention-to-treat principle, medication adherence at 12 months was higher in the PA group than in the PE group (42% vs 36%, respectively; P=.049). The difference, the absolute risk reduction, was 6.25%, which yields a number needed to treat of 16. This means that about 1 in every 16 patients will benefit from the treatment. The within-group reduction in systolic BP for both groups was not statistically significant (2.14 mm Hg for the PA group vs 2.18 mm Hg for the PE group; P=.98); similarly, the within-group reduction in diastolic BP from baseline to 12 months was −1.59 mm Hg for the PA group and −0.78 mm Hg for the PE group (P=.45). Therefore, the PA intervention had a significant impact on medication adherence but not on BP reduction.

Baseline clinical and demographic characteristics compared both groups with t tests or χ2 tests, as appropriate. Adherence data were multimodal and highly skewed, we used a nonparametric Wilcoxon rank sum test to compare the mean adherence rate between both groups at 12 months. For secondary outcome, a standard 2-sample t test compared the mean within-patient change in BP from baseline to 12 months. All analyses were based on the intention-to-treat principle and analyzed with Stata version 10