A student experiment investigating the potential impact of caffeine on studying for a test involved 30 subjects randomly divided into two groups. Each group took 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 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 that 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 soda may aid memory? What other explanation is plausible?