In an experiment to study weight gain in rats, individual rats were fed on one of four different diet types. The types were distinguished by amount of protein (high level or low) and source of protein (beef or cereal). 40 rats were each randomly assigned to a diet type, 10 rats total per type.

After completion of the diets, the following data were obtained:

diet types rat weight gains (in grams)

Beef, low 90, 76, 90, 64, 86, 51, 72, 90, 95, 78

Beef, high 73, 102, 118, 104, 81, 107, 100, 87, 117, 111

Cereal, low 107, 95, 97, 80, 98, 74, 74, 67, 89, 58

Cereal, high 98, 74, 56, 111, 95, 88, 82, 77, 86, 92

a) Three types of designed experiments are mentioned in section 1.6. What type of experiment is this one?

b) Identify the experimental units, the response variable, the factors, and the levels of each factor. Is there an obvious control group?

c) Examine the weight gain data. Which of the diet types, if any, yielded the largest weight gains? Which diet type led to the smallest weight gains?