Exam MAS-I Practice Question 110
Study guide: Exam MAS-I
A study of workers compensation medical costs compares three treatment networks. For each of 30 claims (10 per network) the response is the log of medical cost, and the covariate x is the injured worker's age. Three nested Normal linear models are fitted:
| Model | Residual sum of squares | Residual df |
|---|---|---|
x only |
52.0 | 28 |
x + network (common slope) |
40.0 | 26 |
x \times network (separate slopes) |
37.4 | 24 |
The upper 5% points of the F distribution are F_{0.05}(2, 24) = 3.403 and F_{0.05}(2, 26) = 3.369.
Part a (1 point)
Calculate the F statistic for testing whether the three networks' regression lines are parallel. Give your answer to two decimal places.
Part b (1 point)
Calculate the F statistic for testing whether network affects cost after adjusting for age, assuming a common slope. Give your answer to two decimal places.
Part c (1 point)
At the 5% significance level, which conclusion follows?
- A) The slopes differ by network, so no single network effect can be stated
- B) The lines are parallel, and network has no effect once age is allowed for
- C) The lines are parallel, and network affects cost after adjusting for age
- D) The slopes differ by network, and network has no effect after adjusting for age
- E) No conclusion is possible, because the two tests use different denominators
Answer this question and see the worked solution