Objective: To demonstrate how mixed models may be used to estimate treatment effects, and inform decisions on the need for monitoring initial response.
Study design and setting: Mixed models were used to analyze data from the Perindopril Protection Against Recurrent Stroke Study (PROGRESS), which examined the effects of perindopril and indapamide in 6,105 patients at high risk of a cerebrovascular event.
Results: The mean effect of perindopril was to lower blood pressure (BP) (systolic/diastolic) by 6/3 mmHg. The mean effects of perindopril/indapamide varied according to baseline BP, and lowering of BP ranged from 9/5 to 14/5 mmHg (for individuals with a baseline systolic BP <140 and >150 mmHg, respectively). We found no variation in the effects of treatment on BP for either perindopril alone or in combination with indapamide. The effects of treatment on the individual can be predicted from the mean effect of treatment for the group (perindopril) or baseline systolic BP subgroup (perindopril/indapamide).
Conclusion: Monitoring initial treatment response is unnecessary for antihypertensives similar to those examined in this study. To address this issue for other therapies, we suggest that trials should report estimates of treatment effects from mixed models, and the CONSORT statement should be expanded to include this item.