A researcher predicts that scores in treatment A will be higher than scores in treatment B.If the mean for the 10 participants in treatment A is 4 points higher than the mean for the 10 participants in treatment B and the data produce t = 2.095,what decision should be made?
A)With α = .05, reject H0 for both a one-tailed and a two-tailed test
B)With α = .05, fail to reject H0 for both a one-tailed and a two-tailed test
C)With α = .05, reject H0 for a one-tailed test but fail to reject for a two-tailed test
D)With α = .05, reject H0 for a two-tailed test but fail to reject for a one-tailed test

Question

Quizplus · Accepted Answer

The researcher predicts a directional difference between treatment A and treatment B (i.e. treatment A will have higher scores). Therefore, a one-tailed test is appropriate. The t-value of 2.095 indicates a significant difference between the two groups. With α = .05, the critical t-value for a one-tailed test with 18 degrees of freedom is 1.734. Since the obtained t-value is greater than the critical t-value, we reject the null hypothesis for a one-tailed test. However, for a two-tailed test, the critical t-value is 2.101 (with α = .05 and 18 degrees of freedom). The obtained t-value of 2.095 is not greater than the critical t-value for a two-tailed test, so we fail to reject the null hypothesis for a two-tailed test. Therefore, the correct answer is C: With α = .05, reject H0 for a one-tailed test but fail to reject for a two-tailed test.

A Researcher Predicts That Scores in Treatment a Will Be