Ordinal Predictors in Regression Analysis

Companion webpage to the YouTube video tutorial

Arndt Regorz, Dipl. Kfm. & M.Sc. Psychologie, 05/25/2021

This video shows you different approaches for dealing with an ordinal predictor in a regression analysis. Furthermore, here you can find the full sources for my video.


  1. Video tutorial
  2. Sources for the video

1. Video tutorial

(Note: When you click on this video you are using a service offered by YouTube.)

2. Sources for the video

Walter et al., 1987

Staircase coding of ordinal predictor with several binary variables:

Walter, S. D., Feinstein, A. R., & Wells, C. K. (1987). Coding ordinal independent variables in multiple regression analyses. American Journal of Epidemiology, 125(2), 319-323. https://doi.org/10.1093/oxfordjournals.aje.a114532

Labovitz, 1970

Arguing for treating ordinal predictors as on an interval scale:

Labovitz, S. (1970). The assignment of numbers to rank order categories. American Sociological Review, 35(3), 515-524. https://doi.org/10.2307/2092993

Mayer, 1971

Arguing against treating ordinal predictors as on an interval scale:

Mayer, L. S. (1971). A note on treating ordinal data as interval data. American Sociological Review, 36(3), 519-520. https://doi.org/10.2307/2093098

Williams, 2020

Using mid-points of ordinal categories & testing, whether ordinal scale can be treated as interval:

Williams, R. (2020). Ordinal independent variables. University of Notre Dame. https://www3.nd.edu/~rwilliam/stats3/OrdinalIndependent.pdf

Brown, 2011

Overview over discussion about Likert items and Likert scales with additional sources:

Brown, J. D. (2011). Likert items and scales of measurement. Statistics, 15(1), 10-14. https://hosted.jalt.org/test/bro_34.htm

Wu & Leung, 2017

Recommendation for a 11-point scale (0 to 10) when using a single-item Likert scale:

Wu, H., & Leung, S. O. (2017). Can likert scales be treated as interval scales?—A simulation study. Journal of Social Service Research, 43(4), 527-532. https://doi.org/10.1080/01488376.2017.1329775

Gertheiss & Tutz, 2009

Advanced method: Penalized regression with ordinal predictors:

Gertheiss, J., & Tutz, G. (2009). Penalized regression with ordinal predictors. International Statistical Review, 77(3), 345-365. https://doi.org/10.1111/j.1751-5823.2009.00088.x

Implementation of this method in R:

Gertheiss, J., Hoshiyar, A., & Scheipl, F. (2021). Package 'ordPens' [Reference manual]. CRAN. https://cran.r-project.org/web/packages/ordPens/ordPens.pdf

Gertheiss, J., Scheipl, F., Lauer, T., & Ehrhardt, H. (2022). Statistical inference for ordinal predictors in generalized additive models with application to Bronchopulmonary Dysplasia. BMC Research Notes, 15(1), 1-6. https://doi.org/10.1186/s13104-022-05995-4

Helwig, 2017

Advanced method: Ordinal smoothing splines:

Helwig, N. E. (2017). Regression with ordered predictors via ordinal smoothing splines. Frontiers in Applied Mathematics and Statistics, 3, 15. https://doi.org/10.3389/fams.2017.00015

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