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(Stroke. 2007;38:257.)
© 2007 American Heart Association, Inc.

Letters to the Editor

Deriving Number-Needed-to-Treat and Number-Needed-to-Harm From the Saint I Trial Results

Jeffrey L. Saver, MD

Stroke Center and Department of Neurology, David Geffen School of Medicine at the University of California, Los Angeles, Los Angeles, Calif

An extract of the first 250 words of the full text is provided, because this article has no abstract.

To the Editor:

In their recent publication regarding interpretation of the Stroke-Acute Ischemic NXY Treatment (SAINT I) trial,¹ Koziol and Feng use the definition, but not the derivation method, for number-needed-to-treat (NNT) and number-needed-to-harm (NNH) that was previously described.² As a result they arrive at biologically untenable estimates of NNT and NNH.

A challenge in deriving NNT and NNH values for ordinal scale responses is that parallel group trial results do not specify the within-patient correlation—the degree to which the rank order of patient outcomes is similar under control versus active therapy.² Koziol and Feng implicitly assume that the within-patient correlation is 0. Although this is an approach suggested in the literature,³ for most disease states this assumption is biologically invalid and will result in random person effects being inappropriately counted as treatment effects. This artifact occurs in the analysis of Koziol and Feng, resulting in the derivation of unrealistically low values for the NNT (2.17 to 2.48) and NNH (2.39 to 2.75). These NNT and NNH values indicate that for every 100 patients treated with NXY-059, about 43 improve as a result of therapy and about 39 are harmed as a result of therapy. These estimates are highly implausible. The SAINT results provided evidence of only modest benefit and no evidence of harm of therapy.

Stroke is a condition in which baseline disease severity and other prognostic factors strongly influence the ordering of patient outcomes, under both control and intervention conditions.^4,5 As a result, the within-patient correlation is far . . . [Full Text of this Article]

Related Article:

Response to Letter by Saver

James A. Koziol and Anne C. Feng
Stroke 2007 38: 258. [Extract] [Full Text] [PDF]