Researchers (Brian G. Feagan et al. "Erythropoietin with Iron Supplementation to Prevent Allogeneic Blood Transfusion in Total Hip Joint Arthroplasty," Annals of Internal Medicine, Vol. 133, No. 11) wanted to determine whether epoetin alfa was effective in increasing the hemoglobin concentration in patients undergoing hip arthroplasty. A complete medical history and physical of the patients was performed for screening purposes and eligible patients were identified. The researchers used a computer generated schedule to assign the patients to the high-dose epoetin group, low-dose epoetin group, or placebo group. The study was double-blind. Based on ANOVA, it was determined that there were significant differences in the increase in hemoglobin concentration in the three groups with a P-value less than 0.001. The mean increase in hemoglobin in the high-dose epoetin group was 19.5 grams per liter (g/L), the mean increase in hemoglobin in the low-dose epoetin group was 17.2 g/L, and mean increase in hemoglobin in the placebo group was 1.2 g/L.
(a) Why do you think it was necessary to screen patients for eligibility?
(b) Why was a computer-generated schedule used to assign patients to the various treatment groups?
(c) What does it mean for a study to be double-blind? Why do you think the researchers desired a double-blind study?
(d) Interpret the reported P-value.