Refer to the Animal Science Journal (May, 2014) study on the use of ascorbic acid (AA) to reduce stress in goats during transportation from farm to market, Exercise 9.12. Recall that 24 healthy goats were randomly divided into four groups (A, B, C, and D) of six animals each. Goats in group A were administered a dosage of AA 30 minutes prior to transportation; goats in group B were administered a dosage of AA 30 minutes following transportation; group C goats were not given any AA prior to or following transportation; and, goats in group D were not given any AA and were not transported. Weight was measured before and after transportation and the weight loss (in kilograms) determined for each goat.
a. Write a model for mean weight loss, E(y), as a function of the AA dosage group (A, B, C, or D). Use group D as the base level.
b. Interpret the β's in the model, part a.
c. Recall that the researchers discovered that mean weight loss is reduced in goats administered AA compared to goats not given any AA. On the basis of this result, determine the sign (positive or negative) of as many of the β's in the model, part a, as possible.