7.83 Breast-feeding versus baby formula. A study of iron deficiency among infants compared samples of infants following different feeding regimens. One group contained breast-fed infants, while the infants in another group were fed a standard baby formula without any iron supplements. Here are summary results on blood hemoglobin levels at 12 months of age:39
| Group | n | s | |
|---|---|---|---|
| Breast-fed | 23 | 13.3 | 1.7 |
| Formula | 19 | 12.4 | 1.8 |
(a) Is there significant evidence that the mean hemoglobin level is higher among breast-fed babies? State and and carry out a t test. Give the P-value. What is your conclusion?
(b) Give a 95% confidence interval for the mean difference in hemoglobin level between the two populations of infants.
(c) State the assumptions that your procedures in parts (a) and (b) require in order to be valid.