Topic: Coding Categorical Predictors

Helmert Coding for Ordered Group Comparisons

Factor Levels and Reference Categories

Empty and Unseen Categories in Coded Data

Custom Contrasts for a Planned Group Comparison

Common Indicator-Coding and Labeling Errors

Comparing Coding Schemes in a Three-Group Example

Coding a Two-Level Factor With an Indicator

Choosing a Reference Category for Clear Interpretation

Changing the Reference Category

Calculating Fitted Means for Two Categories