The 'power' of a hypothesis test is a measure of the probability of rejecting the null hypothesis when it is false. The greater the power the more likely that a deviation from the null hypothesis condition will be detected.
The Power varies with the amount that the process varies from the target. The power of a test is its ability to detect a deviation 'δ' from a specified value.
The power of a test is calculated from (1-β ), where β is the probability of a Type II error.