Published 9 June 2009, doi:10.1136/bmj.b2323
Cite this as: BMJ 2009;338:b2323

Letters

Sample size calculations

Must do better

The first 150 words of the full text of this article appear below.

As a reviewer in several study sections at the US National Institutes of Health, I have noted that it is impossible to replicate sample size and power calculations in the overwhelming number of otherwise excellent research proposals.¹ I then noted that replication is very difficult in journal articles.

The sources of sample size calculations, with reference to a specific program or algorithm or to equations and method of calculation, are almost absent from the literature. Rather, the norm can be summarised: "The study has 80% power to detect a 10% difference with an alpha of 0.05." Rarely do authors or proposal applicants specify "using the method of Smith and Jones" or "using the sample size calculator available at ..." and then cite a URL or statistical package. Thus, reviewers cannot ascertain the method used, and the sample size specifications remain only assertions.

Researchers must refer to a specific method, statistical . . . [Full text of this article]

¹ University of Washington, Seattle, WA 98195, USA

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