The power of a test is the probability that the test will find convincing evidence for Ha when a specific alternative value of the parameter is true.Stated another way, power is equivalent to

When a specific alternative value is true, the null hypothesis is false. The power of a test is the probability of rejecting that false null hypothesis, so it means rejecting H0 when you should reject H0. Failing to reject a false H0 is instead a Type II error.

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