The difference between the group means in a pretest-posttest control group experimental design can be tested for statistical significance most precisely by
A) analysis of variance of the groups' means on the posttest.
B) separate t-tests of the prepost difference for the experimental and for the control group.
C) analysis of covariance on the groups' posttest means with pretest as the covariate.
D) analysis of variance of the mean changes from pre- to posttest for the two groups.

Question

Quizplus · Accepted Answer

Analyzing covariance with pretest as the covariate can provide more precise and accurate results by controlling for the pre-existing differences between the two groups. It can help reduce the impact of extraneous variables and increase the accuracy of the results. Option A, on the other hand, only analyzes the posttest means of the groups, which may not be sufficient. Option B separately tests the prepost difference, which may not account for the baseline differences between the groups. Option D analyzes the mean changes but does not control for the pre-existing differences between the groups, which could result in inaccurate results.

The Difference Between the Group Means in a Pretest-Posttest Control