9. Two separate samples, each with n  12 individuals, receive two different treatments. After treatment, the first sample has SS  1740 and the second has SS  1560.

a. Find the pooled variance for the two samples.

b. Compute the estimated standard error for the sample mean difference.

c. If the sample mean difference is 8 points, is this enough to reject the null hypothesis and conclude that there is a significant difference for a two-tailed test at the .05 level?

d. If the sample mean difference is 12 points, is this enough to indicate a significant difference for a two-tailed test at the .05 level?

e. Calculate the percentage of variance accounted for

(r 2

) to measure the effect size for an 8-point mean difference and for a 12-point mean difference.