Comparisonwise error rate

In statistics, during multiple comparisons testing, comparisonwise error rate (also known as pairwise error rate) is the probability of falsely rejecting the null hypothesis for one test, i.e., the probability of Type 1 error occurring. The α (alpha) that is assigned applies to each individual hypothesis test. Cumulative error rate increases rapidly as the number of comparisons increase. Therefore, the number of comparisons to be tested is an important determinant of the most appropriate multiple comparisons method to use.