Topic: Coding Categorical Predictors

Why Recoding Leaves Predictions Unchanged

Why One Category Must Be Omitted

The Intercept as the Reference-Group Mean

Sum Coding for Categorical Predictors

Representing a Factor With K Minus One Indicators

Reading Reference-Coded Regression Output

Reading Sum-Coded Regression Output

Recovering Group Means from Any Coding

Ordered Categories as Factors Rather Than Scores

Interpreting Coefficients Under Sum Coding