A company developing an ad campaign for its cola is investigating the impact of caffeine on studying in hopes of finding evidence of its claim that caffeine helps memory. The firm asked 30 subjects, randomly divided into two groups, to take a memory test. The subjects then each drank two cups of regular (caffeinated) cola or caffeine-free cola. Thirty minutes later they each took another version of the memory test, and the changes in their scores were noted. Among the 15 subjects who drank caffeine, scores fell an average of −0.933 points with a standard deviation of 2.988 points. Among the no-caffeine group, scores went up an average of 1.429 points with a standard deviation of 2.441 points. Assumptions of Normality were deemed reasonable based on histograms of differences in scores.

a) Did scores change significantly for the group who drank caffeine? Test an appropriate hypothesis and state your conclusion.

b) Did scores change significantly for the no-caffeine group? Test an appropriate hypothesis and state your conclusion.

c) Does this indicate that some mystery substance in noncaffeinated cola may aid memory? What other explanation is plausible.