Use both predictors. From the previous two exercises, we conclude that year and soybean yield may be useful together in a model for predicting corn yield. Run this multiple regression.

(a) Explain the results of the ANOVA F test. Give the null and alternative hypotheses, the test statistic with degrees of freedom, and the P-value. What do you conclude?

(b) What percent of the variation in corn yield is explained by these two variables? Compare it with the percent explained in the simple linear regression models of the previous two exercises.

(c) Give the fitted model. Why do the coefficients for year and soybean yield differ from those in the previous two exercises?

(d) Summarize the significance test results for the regression coefficients for year and soybean yield.

(e) Give a 95% confidence interval for each of these coefficients.

(f) Plot the residuals versus year and versus soybean yield. What do you conclude?