An ultramarathon, as you might guess, is a footrace longer than the 26.2 miles of a marathon. RUnners commonly develop respiratory infections after an ultramarathon. Will taking 600 milligrams of vitamin C daily reduce these infections? Researchers randomly assigned ultramarathon runners to receive either vitamin C or a placebo. Separately, they also randomly assigned these treatments to a group of nonrunners the same age as the runners. All subjects were watched for 14 days after the big race to see if infections developed.
(a) What is the name for this experimental design?
(b) Use a diagram to outline the design.