Two weeks ago you did crossover trial of a new experimental treatment for interstitial cystitis. We calculated t tests for carryover and treatment effects, but we have not yet considered period effects. It is unlikely that there are any period effects in this trial, but we may want to test this formally. If there were a period effect, then patient responses under either treatment would likely be systematically higher in one period than the other. (Here’s an analogy: Think of taking the same test twice. You would likely perform better on the test the second time, since you have learned from your experience of taking the first test.) Explain how you would devise a t test for assessing a period effect in this trial. (Hint: look at the explanation of the t test for treatment effects given in the Week Four assignment. There, we based the test on the random variable X – Y. Suppose we look instead at X + Y?)