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(Circulation. 1999;99:377-383.)
© 1999 American Heart Association, Inc.

Clinical Investigation and Reports

Reporting Risks and Benefits of Therapy by Use of the Concepts of Unqualified Success and Unmitigated Failure

Applications to Highly Cited Trials in Cardiovascular Medicine

G. B. John Mancini, MD, FRCP(C); Michael Schulzer, MD, PhD

From the Departments of Medicine (G.B.J.M., M.S.) and Statistics (M.S.), University of British Columbia, and the Vancouver Hospital and Health Sciences Centre, Vancouver, British Columbia, Canada.

Correspondence and reprint requests to Dr G.B. John Mancini, Vancouver Hospital and Health Sciences Centre, Laurel Street Pavilion–Suite 3300, 950 West 10th Avenue, Vancouver, British Columbia V5E 4Z3.

Background—The NNT (number needed to treat) and NNH (number needed to harm) are useful in conveying the results of clinical trials because they emphasize the effort that must be expended to accomplish a single, tangible outcome. But NNT conveys the effort required to achieve a positive outcome without distinguishing between the presence or absence of treatment-related adverse events. Similarly, NNH conveys harm without accounting for the achievement or lack of achievement of the benefit of therapy. Consequently, a mathematical model was developed to extend the NNT and NNH to represent the effort required to achieve "unqualified success" (NNT_US, treatment success without treatment-induced side effects) and "unmitigated failure" (NNH_UF, lack of treatment success with treatment-induced side effects).

Methods and Results—NNT_US was calculated by adjusting the absolute risk reduction to allow for the probability of not incurring a treatment-related adverse event. NNH_UF was similarly calculated by adjusting the absolute risk of incurring a treatment-related adverse event by the probability of not incurring any treatment-related benefit. The impact of conveying clinical trial data by the use of NNT, NNT_US, NNH, and NNH_UF is illustrated by means of 11 highly cited trials identified systematically from the cardiovascular literature. The treatment effort measured by the NNT_US and the NNH_UF was consistently higher than that given by the traditional NNT and NNH. These increments ranged from 1% to several hundred percent.

Conclusions—The NNT_US and the NNH_UF represent the treatment effort required on average to achieve 1 unqualified success and 1 unmitigated failure. NNT_US and NNH_UF balance benefit and harm in an objective way and are relevant for making service delivery decisions.

Key Words: number needed to treat • number needed to harm • clinical trials • unqualified success • unmitigated failure • cardiovascular diseases

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