A researcher wants a 90 percent chance of rejecting the null hypothesis at the one-tailed .05 level with an effect size of .15.The sample size needed is about
A) 140.
B) 160.
C) 180.
D) 200.
E) 380

Question

Quizplus · Accepted Answer

To calculate the sample size needed for this study, we can use a power analysis. Given a target power of .90, a one-tailed alpha level of .05, and an effect size of .15 (which is considered a small effect size), we can use a power analysis calculator or software to determine the necessary sample size.

Using an online calculator (such as G*Power), we find that the sample size needed is approximately 380 participants. This means that if we recruit 380 participants and run our study, we will have a 90% chance of detecting a statistically significant effect (i.e. rejecting the null hypothesis) at the .05 level, assuming the effect size is true.

Therefore, the best choice is E.

A Researcher Wants a 90 Percent Chance of Rejecting the Null