Power in statistical testing is best described as which?

Power in statistical testing is best described as which?

• A. Probability of a Type I error
• B. Probability of not detecting a true effect
• C. Probability of detecting a true effect
• D. Probability of rejecting the null when the null is true

Answer: (C)

Power is a study’s ability to detect a real effect when there is one. It is the probability that the statistical test will reject the null hypothesis given that the alternative is true. In other words, power equals one minus the probability of a Type II error, which is failing to detect a true effect. This is distinct from the probability of making a Type I error, the chance of rejecting a true null (often set by the alpha level). It is also not the probability of rejecting the null when the null is true. Therefore, power best describes the likelihood of detecting a true effect.

Power is a study’s ability to detect a real effect when there is one. It is the probability that the statistical test will reject the null hypothesis given that the alternative is true. In other words, power equals one minus the probability of a Type II error, which is failing to detect a true effect. This is distinct from the probability of making a Type I error, the chance of rejecting a true null (often set by the alpha level). It is also not the probability of rejecting the null when the null is true. Therefore, power best describes the likelihood of detecting a true effect.