Daniel Hackam1 recently summarized the results of a primary prevention trial with lipid-lowering therapy.2 However, these results suffer from a limitation of many reports of randomized controlled trials, in that the benefit is expressed only in terms of the relative risk reduction, which makes it difficult to estimate the total impact of the intervention. Relative risk reduction does not take into account primary and secondary end points, which are expressed by the absolute risk reduction.
A review of the data from the original paper2 indicates that the absolute risk reduction for the primary end point of nonfatal myocardial infarction and fatal coronary artery disease was 1.1%, much more modest than the 36% relative risk reduction that was reported. The number needed to treat (NNT) derived from this absolute risk reduction is 90, which is comparable to the NNT for other prevention trials.3
Presenting absolute as well as relative risk reduction in reports of preventive drug therapy would give practitioners (and their patients) realistic estimates of the potential benefit of specific interventions.
Anthony T. Kerrigan Geriatric Medicine and Respiratory Diseases McMaster University Hamilton, Ont.
References
- 1.Hackam DG. Do hypertensive patients with average cholesterol levels benefit from atorvastatin therapy? CMAJ 2003;168(13):1689. [PMC free article] [PubMed]
- 2.ASCOT investigators. Prevention of coronary and stroke events with atorvastatin in hypertensive patients who have average or lower-than- average cholesterol concentrations, in the Anglo-Scandinavian Cardiac Outcomes Trial — Lipid Lowering Arm (ASCOT-LLA): a multicentre randomised controlled trial. Lancet 2003;361:1149-58. [DOI] [PubMed]
- 3.Shepherd J, Cobbes SM, Ford I, Isles CG, Lorimer AR, MacFarlane PW, et al, for the West of Scotland Coronary Prevention Study Group. Prevention of coronary heart disease with prevastatin in men with hypercholesterolemia. N Engl J Med 1995;333:1301-7. [DOI] [PubMed]