=+18. Here are residual plots (residuals plotted against predicted values) for three linear regression models. Indicate which condition appears to be violated (linearity, outlier, or equal spread) in each case.

a)

–10 0 10 20 30 40 50 60 70 15 10 5

0

–5

–10 Predicted Value Residual b)

15.0 17.5 20.0 22.5 25.0 27.5 30.0 32.5 50 40 30 20 10 0

–10 Predicted Value Residual