Exercise 14.10 described an experiment that involved comparing the completion times associated with four different income tax forms. Suppose the experiment is redone in the following way. Thirty people are asked to fill out all four forms. The completion times (in minutes) are recorded.

a. Is there sufficient evidence at the 1% significance level to infer that differences in the completion times exist between the four forms?

b. Comment on the suitability of this experimental design in this problem.