Use the following data set for Exercises 10–13.
| 18.7 | 2 | 100 | 4.1 |
| 18.4 | 4 | 90 | 5.0 |
| 21.8 | 6 | 90 | 3.8 |
| 22.0 | 8 | 70 | 5.2 |
| 25.2 | 10 | 70 | 3.8 |
| 25.7 | 12 | 50 | 5.3 |
| 26.9 | 14 | 50 | 5.4 |
| 28.3 | 16 | 30 | 5.4 |
| 28.6 | 18 | 30 | 4.3 |
| 31.8 | 20 | 10 | 4.9 |
Question 13.157
13. Verify the regression assumptions for your final model from Exercise 12.
13.99.13
The preceding scatterplot of the residuals versus fitted values shows no strong evidence of unhealthy patterns. Thus, the independence assumption, the constant variance assumption, and the zero-mean assumption are verified. Also, the normal probability plot of the residuals indicates no evidence of departure from normality of the residuals. Therefore we conclude that the regression assumptions are verified.