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Study Design and Statistics

Margaret A. Winker

and Stephen J. Lurie

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Subscriber: null; date: 22 January 2017


UPDATE: We will discontinue using quotation marks to identify parts of an article, but retain the capitalization; eg, This is discussed in the Methods section (not the “Methods” section). This change was made February 14, 2013.

The Results section should include the number of individuals or other data units initially eligible for study, the number at its inception, and the number who were excluded, dropped out, or were lost to follow-up at each point in the study. For example, JAMA requires a figure showing the flow of participants through controlled trials (see 20.2, Randomized Controlled Trials). Authors should provide descriptive statistics about the sample and, if appropriate, the individual subgroups. Primary outcome measures should be discussed after the study population is described, followed by secondary outcome measures. Post hoc analyses may be presented, but they should be identified as such. Results of post hoc analyses may be unreliable, and thus such analyses should be used for generating rather than testing hypotheses (see type I error). If one statistical test has been used throughout the manuscript, the test should be clearly stated in the Methods section. If more than one statistical test has been used, the statistical tests performed should be discussed in the methods and the specific test used reported along with the corresponding results. Tests of relative results (eg, relative risk, odds ratio) may overstate the real magnitude of differences between groups, particularly when such values are very small. Thus, when presenting relative results, authors should also report a measure of the actual central tendency of the groups (ie, mean or median).

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