Statistical Power

Type II error refers to the probability of failing to reject a null hypothesis when it is false. Then, statistical power refers to the probability of rejecting the null hypothesis when it is false. The following figure shows that the size of Type II error is measured by the area of β in the alternative sampling distribution when the null hypothesis is false, and the alternative hypothesis is true. In the context of the following figure, the statistical power of the test refers to 1 − β, which equals the remaining area of the alternative sampling distribution under the alternative hypothesis. Power analysis is important for experimental studies, particularly in medicine and epidemiology.