How do you choose to argue? Refer to the Thinking and Reasoning (Oct. 2006) study of the cognitive skills required for successful arguments, presented in Exercise 9.25 (p. 479). Recall that 52 psychology graduate students were equally divided into two groups. Group 1 was presented with arguments that always attempted to strengthen the favored position. Group 2 was presented with arguments that always attempted to weaken the nonfavored position. Summary statistics for the student LO3 ratings of the arguments are reproduced in the accompanying table. In Exercise 9.25, you compared the mean ratings for the two groups with a small-sample t-test, assuming equal variances. Determine the validity of this assumption at a = .05.

Group 1

(support favored position)

Group 2

(weaken opposing position)

Sample size 26 26 Mean 28.6 24.9 Standard deviation 12.5 12.2