In a randomized trial, a planned crossover design:
a. Eliminates the problem of a possible order effect
b. Must take into account the problem of possible residual effects of the first therapy
c. Requires stratified randomization
d. Eliminates the need for monitoring compliance and noncompliance
e. Enhances the generalizability of the results of the study
Answer: b. Must take into account the problem of possible residual effects of the first therapy