.McAllister et al. (2012) compared college football and hockey players with college athletes playing non-contact sports to determine if exposure to head impacts over the course of a season had an effect on cognitive performance. In the study, testing new learning performance was significantly worse for athletes playing contact sports than for those playing non-contact sports. The following table presents data similar to the results obtained in the study. Athletes (Non-contact sport) Athletes (Contact sport) 11 8 9 5 8 10 10 4 14 8 8 7 7 11 13 3

a) Choose your hypothesis test, do your calculations and answer this question: Are the results of athletes practicing contact sports

significantly lower than those of athletes practicing non-contact sports? (Use a one-sided test with an alpha of 0.05.)

b) Calculate the value of r2 (the percentage of variance explained by these data) and give its interpretation. c) Suppose that your samples are not equal, and that in the list corresponding to athletes with contact, you are missing 2 values. What approach can you use to work around this problem?