=+a) The state with the highest leverage and largest Cook’s Distance is Alaska. It is plotted with an x in the residuals plot. Here are a scatterplot of the residuals, a normal probability plot of the leverage values, and a histogram of Cook’s distance values. What evidence do you have from these diagnostic plots that Alaska might be an influential point?

–1 0

1 Residuals Predicted 69 70 71 72

–1.25 0.00 1.25 Nscores Leverages 0.300 0.225 0.150 0.075 0.00 Cook’s Distance 0.25 0.50 50 40 30 20 10 Here’s another regression with a dummy variable for Alaska added to the regression model.

Dependent variable is: Life exp R-squared = 70.8% R-squared (adjusted) = 67.4%

s = 0.7660 with 50 - 6 = 44 degrees of freedom Source Sum of Squares df Mean Square F-ratio Regression 62.4797 5 12.4959 21.3 Residual 25.8193 44 0.586802 Variable Coeff SE(Coeff) t-ratio P-value Intercept 67.6377 1.480 45.7 60.0001 Murder -0.250395 0.0426 -5.88 60.0001 HSGrad 0.055792 0.0212 2.63 0.0116 Illiteracy 0.458607 0.3053 1.50 0.1401 Income 3.68218e-4 0.0003 1.46 0.1511 Alaska -2.23284 0.9364 -2.38 0.0215