A study was designed to compare the effect of a vitamin E supplement on the growth of guinea pigs. There were 15 guinea pigs available for the study. The guinea pigs were randomly assigned to one of the three dose levels of vitamin E with 5 animals per level. For each animal, the body weight was recorded at the end of weeks 1, 3, 4, 5, 6, and 7. All 15 animals were given a growth- inhibiting substance during week 1 and given identical diets during the first four weeks of the study. At the beginning of week 5, the vitamin E treatments were implemented. The three treatment levels (doses of vitamin E) were 0, L (low), and H (high). The data include the response variable WEIGHT for each of the 15 animals for each of the 6 weekly weighings (total of 90 measurements). The other information available for each observation is the levels of DOSE (0, L, and H) and the WEEK (1, 3, 4, 5, 6, and 7). The animals are numbered 1 through 15. In addition, a variable called BEFAFT is created, which has the following values:
BEFAFT = B for weeks 1, 3, and 4—that is, before the start of the vitamin E doses
BEFAFT = A for weeks 5, 6, and 7—that is, after starting the vitamin E doses Nutrition