Question

"A producer of various feed additives for cattle conducts a study of the number of days of feedlot time required to bring beef cattle to market weight. Eighteen steers of essentially identi- cal age and weight are purchased and brought to a feedlot. Each steer is fed a diet with a specific combination of protein content, antibiotic concentration, and percentage of feed supplement. The data are as follows:

STEER   PROTEIN ANIBIO  SUPPLEM TIME
1       10      1       3       88
2       10      1       5       82
3       10      1       7       81
4       10      2       3       82
5       10      2       5       83
6       10      2       7       75
7       15      1       3       80
8       15      1       5       80
9       15      1       7       75
10      15      2       3       77
11      15      2       5       76
12      15      2       7       72
13      20      1       3       79
14      20      1       5       74
15      20      1       7       75
16      20      2       3       74
17      20      2       5       70
18      20      2       7       69

8. Calculate the coefficient of determination and interpret.

9. Suppose x1 = PROTEIN, x2 = ANTIBIO and x3 = SUPPLEM, and you enter these predictors in the model in the order of x1, x2, x3. Find SSR(x2 | x1) and SSR(x3 | x1, x2). What do they mean?

10. Test whether adding ANTIBIO and SUPPLEM provides any additional predictive value, given that PROTEIN is already in the model. Include all steps of a statistical test.

Answer 1