Role of controlled trials in evaluating preventive medicine procedures

A number of large controlled trials evaluating methods of preventing cardiovascular disease are reviewed, mainly for their methodological lessons. They include trials of treatment for hypertension (Veterans Administration, Australian, and the Hypertension Detection and Follow-up Program); of coronary heart disease prevention by drugs (post-infarction beta-blockers, the WHO trial of clofibrate, and the Lipid Research Clinics Program); and of health education (the Multiple Risk Factor Intervention Trial and the WHO European Multifactorial Trial). Although important evidence has emerged, expectations from large trials of this kind are now more sober. Their findings have to be considered alongside the rest of the evidence, and preventive policy can only be based on a best judgment. Any hope of 'proof' is naive.