Problems
All problems below concern the Fish DDT data set of Appendix III from the textbook. You can find these data on-line---start from the STA113 home page and look for the Data pages. In fact the same data are there in three different formats; use whichever one you prefer, they all have the same data. Use the entire 144 observation dataset.
Problem 1
| a) | Plot Weight vs. Length for these data. |
| b) | Find the regression intercept and slope coefficients b0 and b1 (use Minitab or S-Plus), and add the regression line to your plot from a) above |
| c) | Plot the residuals of this regression vs. the fitted values. |
| d) | Do the residuals suggest that any of the regression assumptions were violated? Comment. |
Problem 2
| a) | Plot log(Weight) vs. Length for these data (Hint: Explore Minitab's commands LET and LOG). |
| b) | Find the regression coefficients and add the regression line to your plot. |
| c) | Plot the residuals of this regression vs. the fitted values. |
| d) | Do the residuals suggest that any of the regression assumptions were violated? Comment. |
| e) | Which regression seems (from Problem 1 or Problem 2) seems better? Why? |
Problem 3
| a) | Invent a new variable |
| b) | Find INTERVAL estimates (with alpha=.95) for the regression coefficients for modelling DDT as a linear function of weight, length, and CF. |
| c) | Do DDT levels for catfish differ from those for other fish? Justify your conclusion. |