Background: The complier average causal effect (CACE) analysis addresses noncompliance with intervention and missing end-point measures in randomized controlled trials.
Objectives: To conduct a CACE analysis for the Peer Coach and Office Staff Support Trial examining the intervention's effect among "compliers," defined as subjects who would have received an effective dose of the intervention had it been offered, and to compare with an intention-to-treat analysis.
Research design and subjects: A randomized controlled trial of 280 African American patients aged 40-75 with sustained uncontrolled hypertension from 2 general internal medicine practices.
Measures: Change in 4-year coronary heart disease (CHD) risk (primary) and in systolic blood pressure (SBP) (secondary) from the baseline to the end of the 6-month intervention.
Results: Of 136 intervention subjects, 68% were compliers who had significantly more end points measured (86% vs. 34% for CHD risk; 99% vs. 57% for SBP) and lower baseline CHD risk (5% vs. 7.5%) and SBP (139 vs. 144 mm Hg) compared with noncompliers. In the intention-to-treat analysis, the effect of offering the intervention was nonsignificant for 4-year CHD risk (P=0.08) but significant for SBP (P=0.003). CACE analyses showed that receipt of an effective dose of the intervention resulted in a 1% greater reduction in 4-year CHD risk (P<0.05) and at least 8.1 mm Hg greater reduction in SBP compared with compliers in the control group (P<0.05).
Conclusions: Among compliers, an effective dose of peer coach and office-based support resulted in significant reductions in 4-year CHD risk and SBP. More intensive interventions are likely to be required for noncompliers.