175-179 ........ Discursive introduction. 181-183 ........ Comparing two groups ignoring other variables. 184-185 ........ Establishing that Salary is related to both Rating and InHouse. 186 ........ Visualizing a line for each group. 187 ........ Fitting the dummy variable regression (the parallel slopes model). 188-189 ........ Interpreting the output from a dummy variable regression. 190-191 ........ Basic regression diagnostics for the model. 192-193 ........ Fitting the dummy variable regression (non-parallel slopes model -- interaction/cross product term) 194-195 ........ Basic regression diagnostics for the interaction model. 196-197 ........ Adding a third variable.