Download from the text website the data file Crabs.dat introduced in Section 1.5.1. Fit the linear model with both weight and color as explanatory variables for the number of satellites for each crab, without interaction, treating color as qualitative. Summarize and interpret the software output, including the prediction equation, error variance, R2, adjusted R2, and multiple correlation.

Plot the residuals against the fitted values for the model, and interpret. What explains the lower nearly straight-line boundary? By contrast, what residual pattern would you expect if the response variable is normal and the linear model holds with constant variance?