An article in the Journal of Environmental Engineering (Vol. 115, No. 3, 1989, pp. 608€“619) reported the results of a study on the occurrence of sodium and chloride in surface streams in central Rhode Island. The following data are chloride concentration y (in milligrams per liter) and roadway area in the watershed x (in percentage).




(a) Draw a scatter diagram of the data. Does a simple linear regression model seem appropriate here?
(b) Fit the simple linear regression model using the method of least squares. Find an estimate of σ2.
(c) Estimate the mean chloride concentration for a watershed that has 1% roadway area.
(d) Find the fitted value corresponding to x = 0.47 and the associated residual.

Transcribed Image Text:

4.4 6.6 9.7 10.6 10.8 10.9 0.19 0.15 0.70 0.63 0.57 0.67 11.8 12.1 14.3 14.7 15.0 17.3 0.78 0.47 0.70 0.60 0.78 0.81 23.1 27.4 27.7 19.2 31.8 39.5 0.69 1.30 1.05 1.06 1.74 1.62