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January 6, 1999

Evaluating Reporting and Abstracts of Clinical Trials

Author Affiliations

Margaret A.Winker, MDIndividualAuthorPhil B.FontanarosaMD, Senior EditorsIndividualAuthor

JAMA. 1999;281(1):34-35. doi:10-1001/pubs.JAMA-ISSN-0098-7484-281-1-jbk0106

To the Editor: We congratulate Dr Scherer and Ms Crawley1 for the first published study to use the Consolidated Standards of Reporting Trials (CONSORT) statement as an instrument to systematically evaluate the quality of the reporting of clinical trials. However, we have some methodological concerns regarding this study.

The authors did not prospectively estimate the sample size that would have resulted in adequate power, and they fail to emphasize the low power as an important limitation, especially since the study in general failed to find significant differences in regard to its hypotheses. The authors mention that "it is possible that our sample size was insufficient to detect subtle changes in reporting," suggesting incorrectly that there was adequate power to detect meaningful changes. Power was further limited by the fact that proportions of certain potential confounders were significantly different across journals; comparisons were made separately for each journal, further lowering the sample size. For example, Ophthalmology had the largest sample size of 51 articles, 28 of which had structured abstracts and 23 did not. If a criterion was met in 50% of the articles without structured abstracts and if a 25% difference (ie, 50% greater or lesser than that in articles without structured abstracts) was considered to be meaningful, then the study had only 34% power to detect this difference, even without correcting for multiple comparisons. For comparisons in the Archives of Ophthalmology, the power was even lower because the sample size was only 26.