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(Stroke. 2009;40:2295.)
© 2009 American Heart Association, Inc.

Editorials

Treating Patients With Ischemic Stroke With Tissue Plasminogen Activator in the 3.5- to 4-Hour Window

Numbers Support Benefit but the Message Is to Still Go Fast

Tobias Kurth, MD, ScD Christophe Tzourio, MD, PhD

From the INSERM Unit 708-Neuroepidemiology (T.K., C.T.) and Faculty of Medicine, University Pierre et Marie Curie, Paris, France; Division of Preventive Medicine (T.K.), Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Mass; Department of Epidemiology (T.K.), Harvard School of Public Health, Boston, Mass.

Correspondence to Tobias Kurth, MD, ScD, INSERM Unit 708– Neuroepidemiology, Hôpital de la Pitié-Salpêtrière, 47 boulevard de l’Hôpital, 75651 Paris Cedex 13, France. E-mail tobias.kurth@upmc.fr

Key Words: methodology • stroke care • tissue plasminogen activator

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

See related article, pages 2433–2437.

Numbers needed to treat (NNT) is a powerful tool that has been proposed to translate research findings of treatment effects to an intuitive figure for clinical settings or for policy-making purposes. It is a measure of clinical benefits that describes the number of individuals who would need to be treated to prevent the occurrence of 1 outcome event.¹ NNT, most commonly, is simply calculated by the inverse of the absolute risk difference between 2 treatment options.

However, important limitations should be considered when using NNT in communicating research findings. First, as with all relative or absolute treatment effect measures, causality must be assumed, which even in the setting of randomized controlled trials is not guaranteed if, for example, compliance or follow-up rates differ according to treatment groups or blinding of treatments cannot be achieved. Second, NNT is specific to a comparison of treatment effects in 1 study population. Thus, it should be considered specific to a particular comparison and not necessarily to a particular therapy.² Strictly speaking, NNT only applies to patients of a specific trial and the application of this NNT to any other setting is an extrapolation, which may or may not be valid. Third, the NNT will vary across groups with different baseline risks for the outcome, even if the overall drug effect is similar across groups.³ As an example, a meta-analysis of the effect of antihypertensive drugs on mortality is often used in which the NNT for antihypertensive therapy to . . . [Full Text of this Article]

Related Article:

Number Needed to Treat to Benefit and to Harm for Intravenous Tissue Plasminogen Activator Therapy in the 3- to 4.5-Hour Window: Joint Outcome Table Analysis of the ECASS 3 Trial

Jeffrey L. Saver, Jeffrey Gornbein, James Grotta, David Liebeskind, Helmi Lutsep, Lee Schwamm, Phillip Scott, and Sidney Starkman
Stroke 2009 40: 2433-2437. [Abstract] [Full Text] [PDF]