Two researchers separately testing the same research hypothesis end up with the same sample size (Ni = 12) and standard deviations for the two groups (s1 = .50 and s2 = .75). However, the experimental manipulation is more effective for the second researcher, which results in a bigger difference between the means of the two groups: X ¯ 1 = 2.50 and X ¯ 2 = 2.15 (first researcher), as well as X ¯ 1 = 2.70 and X ¯ 2 = 1.95 (second researcher).
a. Calculate the standard error of the difference (s X ¯ 1 − X ¯ 2) and the t-test for independent means for each study.
 b. How does the increased between-group variability in the second study affect the calculated value of the t-statistic, as well as the probability of making a Type II error?
