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(Circulation. 2000;101:e98.)
© 2000 American Heart Association, Inc.

Circulation Electronic Pages

Qualification of the Concepts of Unqualified Success and Unmitigated Failure

Kenneth M. Kessler, MD

Professor of Medicine University of Miami School of Medicine, Miami, FL

	Introduction

 
To the Editor:

By mathematically compensating for adverse effects, Mancini and Schulzer¹ refine the concept of the numbers needed to be treated (NNT) for a therapeutic success and introduce the use of the terms: (1) the numbers needed to be treated for an unqualified success (NNT_US) or (2) an unmitigated failure (NNH_UF). Nevertheless, there appear to be important limitations to these concepts. First, the authors define an unqualified success as "...a successful outcome unaccompanied by treatment-related adverse events...". However, in the context of practice, as one moves from the NNT to the NNT_US, more adverse events will occur (eg, in the first study in the Table shown in the article, the NNT of 58.82 would be associated with 1.18 adverse events, whereas the NNT_US of 60.02 would be associated with a proportionate increase in adverse events to 1.20). The only time a success would truly be unqualified would be if there were no adverse events associated with a given therapy, but then the calculation of the NNT_US would become unnecessary. Second, neither the NNT_US nor the NNH_UF compensates for the adverse events that occur in the proportion of the population who cannot benefit from treatment. This is an essential concept since (1) these patients will be harmed never having had the possibility of benefit (they are, in essence, bystanders) and (2) the majority of adverse events will emanate from this portion of the population whenever p₁ is <50%. Again using the authors’ first example in the Table, . . . [Full Text of this Article]