Question

Problem 4. Once again you will be using the EXPRESS data set. The first 10 observations are given for illustrative purposes.

Weight	Distance	Cost
5.9	47	2.6
3.2	145	3.9
4.4	202	8
6.6	160	9.2
0.75	280	4.4
0.7	80	1.5
6.5	240	14.5
4.5	53	1.9
0.6	100	1
7.5	190	14

a) Write out a complete general first-order model including an interaction term for Cost as the outcome.

b) Using Minitab, fit a model including the interaction term. Paste your output here.

c) Write the least squares regression equation with the interaction term.

d) State the null and alternative hypothesis to test if there is a significant interaction effect between weight and distance. Test the hypothesis at the α= 0.01 level. Write your formal conclusion in terms of the variable names.

e) If there is a significant interaction effect, but the individual predictors (main effects) that make up that interaction are not significant in the model, would you suggest removing the main effects? Why or why not?

Answer 1