Class 6. Categorical variables: 2-levels.

Table of contents for Class 6

	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.