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Nutrition and Health (including climate and ecological aspects)

Statistical analysis of continuous outcomes from parallel-arm randomized controlled trials in nutrition—a tutorial

European Journal of Clinical Nutrition volume 75, pages 160–171 (2021)Cite this article

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A Correction to this article was published on 14 October 2020

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Abstract

Randomized controlled trials (RCTs) play a fundamental role in establishing evidence on benefits of diet changes in nutrition. There is, however, little literature on how to analyze data obtained from such trials. This tutorial provides a detailed introduction to the statistical analysis of parallel-arm RCTs in nutrition by means of modern statistical methodology, i.e., analysis of covariance and linear mixed models are informed using specific information about the trial design. Focus will be on understanding how the trial design and possibly other aspects of the trial influence the subsequent statistical analysis. All steps of the statistical analysis will be covered and a practical example is also provided.

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Fig. 1: Two scatter plots showing covariate effects on an outcome.
Fig. 2: Revisiting Fig. 1, now showing covariates effects on an outcome separately for each dietary intervention group.
Fig. 3: Two plots showing changes in systolic blood pressure for 16 participants from baseline to end of study.
Fig. 4: Revisiting Fig. 3, now showing the different effects that the outcome is decomposed into.

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Code availability

In practice the specification of the above-mentioned statistical models depends on the statistical software used. A detailed example using the statistical environment R [42] is provided as online supplementary material (https://doi.org/10.5281/zenodo.3978040).

Change history

  • 14 October 2020

    In the original version of this article, the legends to Figs. 2, 3 and 4 were inadvertently swapped. This has now been corrected in the PDF and HTML versions of the article.

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  1. Department of Nutrition, Exercise and Sports, University of Copenhagen, Rolighedsvej 26, DK-1958, Frederiksberg C, Denmark

    Christian Ritz

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Ritz, C. Statistical analysis of continuous outcomes from parallel-arm randomized controlled trials in nutrition—a tutorial. Eur J Clin Nutr 75, 160–171 (2021). https://doi.org/10.1038/s41430-020-00750-z

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