Crohn’s disease involves chronic inflammation anywhere in the gastrointestinal (GI) tract. The disease is subdivided by where it occurs in the GI tract. Suppose a company is testing a new time-release drug to help alleviate the symptoms of Crohn’s disease in a placebo-controlled experiment. They recruit 300 volunteers; 120 of these have the disease in their small intestine, 100 have it in both their small intestine and colon, and 80 have it confined to just their colon. 

a. What variable would you block on in this experiment? 

b. How would you use a randomized block design to randomly assign the subjects in this study? 

c. What is the advantage of using a randomized block design over a completely randomized design?