There has been proposed several strategies to select an article under the assumption of quality and relevance. Mostly depend on the presence or absence of a number of features and others, depends of the judgment of other people. However, these strategies do not allow us to know the magnitude of the error contained within each article. And considering that there is not a perfect one, it is important to identify the magnitude of the error and the impact of this in the final result; consequently,

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... t is necessary to develop skills that allow us to review a paper, identify potential errors, and generate a sense of the impact of it over the result. Using the information contained in Clinical Research Series I-VII, we have tried to show its application in a structured review of an article of causality beginning with the revision of the baseline, the maneuver and the outcome, with systematic errors (bias) generated in each section, followed by the appropriate of the statistical test and the sample size used, and finally, the clinical relevance.