Weighted Effect Coding for Observational Data with wec

Authors

Rense Nieuwenhuis, Stockholm University
Manfred te Grotenhuis, Radboud University
Ben Pelzer, Radboud University

Date of this Version

6-2017

Document Type

Article

Citation

The R Journal (June 2017) 9(1); Editor: Roger Bivand

Comments

Copyright 2017, The R Foundation. Open access material. License: CC BY 4.0 International

Abstract

Weighted effect coding refers to a specific coding matrix to include factor variables in generalised linear regression models. With weighted effect coding, the effect for each category represents the deviation of that category from the weighted mean (which corresponds to the sample mean). This technique has particularly attractive properties when analysing observational data, that commonly are unbalanced. The wec package is introduced, that provides functions to apply weighted effect coding to factor variables, and to interactions between (a.) a factor variable and a continuous variable and between (b.) two factor variables.