In DB3, the mean for the 16 patients' differences between baseline and 5-day serum theophylline level is 0.993 mg/dl, with standard deviation 3.485. For such a difference to be significant with a = 0.05 and power =

0.80, n = 50 pairs would be required [using a formula slightly different from Eq. (7.2) that can be found in Chapter 22]. Generating 3 random samples of 50 on a computer from a normal distribution with the same mean and standard deviation, we find t tests yielding p-values of 0.040, 0.042, and 0.072. Comment on the adequacy of the estimated minimum sample size.