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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.

Original publication




Journal article


Am j clin nutr

Publication Date





991 - 994


Guidelines as Topic, Humans, Nutritional Sciences, Randomized Controlled Trials as Topic, Statistics as Topic, United Kingdom