The Use of Carpeting in Hospitals, While Having Aesthetic Value

The use of carpeting in hospitals, while having aesthetic value, raises an obvious question: Are carpeted floors sanitary? An experiment comparing airborne bacteria levels in carpeted rooms with that in uncarpeted rooms was performed in an effort to answer this question. Specifically, for each of eight carpeted rooms and eight uncarpeted rooms in a hospital, the number of bacteria per cubic foot of air was measured. The data are given below. Assume that room sizes are equal, and that the 16 rooms in this experiment were assigned randomly to the carpet and no-carpet groups. The researcher is interested in testing H₀ : no difference in distribution of bacteria counts for carpeted and uncarpeted rooms, against the one-sided alternative H _a^: the carpeted group tends to have higher bacteria counts. If W, the Wilcoxon rank sum test statistic, is the sum of the ranks assigned to the carpeted group, then the P-value for the test is:

A) 0.046.
B) 0.248.
C) 0.496.
D) 0.752.