Question: Problem 15 in Chapter 10 described a study by Laughlin, Zander, Knievel, and Tan (2003) showing that groups of three people consistently outperformed the best of the individuals working alone on a letters-to-numbers substitution problem. The following data describe the number of trials needed to solve each problem for a sample of n = 15 groups and a sample of n = 15 individuals.

GROUPS INDIVIDUALS

n = 15 n = 15

M = 3.8 M = 4.7

SS = 15.4 SS = 18.2

a. Make a point estimate of how much better groups perform than individuals for the general population. (Estimate the mean difference in the number of trials needed for a solution.)

b. Make an interval estimate of the mean difference so that you are 95% confident that the true mean difference is in your interval. c. Based on your answer to part b, what would be the decision from a hypothesis test evaluating the significance of the mean difference using a two-tailed test with α .05. Explain your answer.