# An article in the Journal Environmental Engineering Division describes the results of testing a s…

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An article in the Journal Environmental Engineering Division describes the results of testing a sample from the Holston River below Kingport, during August 1977, The biochemical oxygen demand (BOD) test is conducted over a period of time in days. The resulting data is shown here: Assuming that a simple linear regression model is appropriate, fit the regression model relating BOD (y) to the time (x). What is the estimate of sigma^2? What is the estimate of expected BOD level when the time is 15 days? What change in mean BOD is expected when the time increase by 3 days? Calculated the fitted y_i for each value of x_i used to fit the model. Then construct a graph of fitted y_i versus the corresponding observed y_i and comment on what this plot would look like the relationship between y and x was a deterministic (no random error) straight line. Does the plot indicate that time is an effective regressor variable in predicting BOD?