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JAMA Guide to Statistics and Methods
February 7, 2019

Number Needed to Treat: Conveying the Likelihood of a Therapeutic Effect

Author Affiliations
  • 1Department of Neurology, Ronald Reagan–UCLA Medical Center and David Geffen School of Medicine, University of California, Los Angeles
  • 2Department of Emergency Medicine, Harbor-UCLA Medical Center, Torrance, California
  • 3Department of Emergency Medicine, David Geffen School of Medicine, University of California, Los Angeles
  • 4Berry Consultants LLC, Austin, Texas
JAMA. 2019;321(8):798-799. doi:10.1001/jama.2018.21971

Effectively communicating clinical trial results to patients and clinicians is a requirement for appropriate application in clinical practice. In a recent issue of JAMA, Zhao et al1 reported the results from a randomized clinical trial comparing dual antiplatelet therapy with aspirin monotherapy for preserving saphenous vein graft patency in 500 patients undergoing coronary artery bypass grafting. Dual antiplatelet therapy was found to be superior to aspirin monotherapy. The authors1 used the number needed to treat (NNT) to communicate effect size, reporting that for every 8 patients treated with dual agents rather than aspirin alone, 1 additional patient would achieve saphenous graft patency at 1 year. The NNT may be defined as the number of patients who need to be treated with one therapy vs another for 1 additional patient to have the desired outcome. Since its first description 30 years ago,2 the NNT has become an important means to express the magnitude of benefit conferred by a therapy.3