27. The purpose of a study by Thurnau et al. (A-30) was to evaluate the accuracy of the fetal—pelvic index disproportion and delivery outcome in gravid women attempting vaginal birth after previous cesarean delivery. Among the data reported were the following on birth weight (grams):
Delivery Outcome n Mean Standard Deviation Cesarean delivery 18 3486 393 Vaginal delivery 47 3325 514 Construct a 95 percent confidence interval for the difference in population means. State the assumptions that make your procedure valid.