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Researchers often analyze randomized trials and other comparative studies by separate analysis of changes from baseline in each parallel group. This may be the only analysis presented or it may be in addition to the direct comparison of allocated groups. We illustrate this by reference to 3 recently published nutritional trials. We show why this method of analysis may be highly misleading and may produce type I errors far greater than the 5% that we expect. We recommend direct comparison of means between groups with the use of baseline as a covariate if required.


Journal article


The American journal of clinical nutrition

Publication Date





991 - 994


Department of Health Sciences, University of York, York, United Kingdom; and


Humans, Great Britain, Nutritional Sciences, Statistics as Topic, Randomized Controlled Trials as Topic, Guidelines as Topic