Post hoc analysis
In the design and analysis of experiments, post hoc analysis (from Latin post hoc, "after this") consists of looking at the data—after the experiment has concluded—for patterns that were not specified a priori. This typically creates a multiple testing problem. That is, each time a pattern in the data is considered, a statistical test is effectively performed. Multiple testing procedures are sometimes used to compensate, but that is often difficult or impossible to do precisely. Post hoc analysis that is conducted and interpreted without adequate consideration of this problem is sometimes called data dredging by critics because the more one looks the more likely something will be found.