Several statistical tests done on the same observations.
Note: In a study, the sample size and the alpha level are set according to the principle that a single null hypothesis will be tested at the end of the study, once all the data have been gathered. If more than one statistical test is undertaken, e.g. pairwise comparisons of several interventions, or tests on different variables, at different timepoints or on different sub-groups, there will be an increase in the planned overall Type I error (alpha) probability. Some statistical methods are proposed to take multiple testing into account, but they are controversial.