Question

Do one-tailed and two-tailed hypotheses differ in relation to statistical power?

Answer 1

Statistical Power is the probability of rejecting the null hypothesis when, in fact, it is false.

One-tailed tests have more statistical power to detect an effect in one direction than a two-tailed test with the same design and significance level. One-tailed tests occur most frequently for studies where one of the following is true:

i) Effects can exist in only one direction.

ii) Effects can exist in both directions but the researchers only care about an effect in one direction. There is no drawback to failing to detect an effect in the other direction.