Matched Pairs Examples:
Suppose we want to determine whether a vitamin C regime reduces the occurrence of the common cold. Our subjects are identical twins. One twin would be randomly assigned a daily dose of vitamin C , the other would be assigned a placebo.
2. Before and after studies (subject is same in both treatments)
We want to study the effect of a weight loss program. Each subject in weighed before they begin the program and then after they finish the program.