Electrical Measurements of Nerve Activity Give a Clue to the Nature

Short Answer

Electrical measurements of nerve activity give a clue to the nature of poisoning with the insecticide DDT. When a nerve is stimulated, its electrical response shows a sharp spike, which is followed by a much smaller second spike. In a randomized experiment, researchers measured the relative height of the second spike as a percent of the first spike, comparing 6 rats poisoned with DDT and a control group of 6 unpoisoned rats. Here are the findings:
$$\begin{array} {| l | l l l l l l| } \hline \text { Poisoned } & 8.456 & 12.207 & 16.869 & 20.589 & 22.429 & 25.050 \\\hline \text { Unpoisoned } & 6.642 & 8.182 & 9.351 & 9.686 & 11.074 & 12.064 \\\hline\end{array}$$
Let W, the Wilcoxon rank sum test statistic, be the sum of the ranks assigned to the relative spike height in rats poisoned with DDT.
If the two populations have the same continuous distribution, what is the mean of W?