Family-wise Type I Error:
In multiple comparison procedures, family-wise type I error is the probability that, even if all samples come from the same population, you will wrongly conclude that at least one pair of populations differ.
If is the probability of comparison-wise type I error, then the probability
where C is the total number of pairwise comparisons for k populations:
For example, for k=4 populations, there are C=6=4(4-1)/2 pairs of populations; and for
See also: Bonferroni adjustment.