A Study Was Conducted to Assess the Effects of Caffeine

Multiple Choice

A study was conducted to assess the effects of caffeine on concentration. Fifteen subjects were recruited into the study and randomly divided into three groups of equal sample size. Group 1 was given an 8-ounce cup of coffee; group 2, an 8-ounce cup of black tea; and group 3, an 8-ounce cup of decaffeinated coffee. Each subject was then shown a set of 20 numbers for one minute. The subjects were then asked to enter five of the numbers they had been shown and the time it took was recorded. A statistician told the investigators they should use a nonparametric test, since their data was unlikely to be Normally distributed and their sample was small. The researchers consulted the literature on nonparametric tests and found several. An appropriate test to use here is:

A) the Wilcoxon signed rank test.
B) the Kruskal-Wallis test.
C) the Wilcoxon rank sum test.
D) the Mann-Whitney test.