If we have a 10-test in a population having equal means. • If a significant level α=0.05, the probability of failing to reject a hypothesis of no difference in each case=0.95 • The probability failing to reject a hypothesis of no difference all 10 tests is (0.95)10 =0.5987 • Then, the probability of rejecting at least one hypothesis of no difference will be 1-0.5987 = 0.4013 • This is a type I error.