Question: One of the primary advantages of a repeated-measures design compared to independent-measures, is that it reduces the overall variability by removing variance caused by individual differences. The following data are from a research study comparing two treatment conditions.

a. Assume that the data are from an independent-measures study using two separate samples, each with n = 6 participants. Compute the pooled variance and the estimated standard error for the mean difference.

b. Now assume that the data are from a repeated-measures study using the same sample of n = 6 participants in both treatment conditions. Compute the variance for the sample of difference scores and the estimated standard error for the mean difference. (You should find that the repeated-measures design substantially reduces the variance and the standard error.)

Treatment 1 Treatment 2 Difference

10 13 3

12 12 0

8 10 2

6 10 4

5 6 1

7 9 2

M=8 M = 10 Ma = 2

SS=34 SS=30 SS=10