Non-linear relationships in clinical research

Nephrology Dialysis Transplantation, vol. 40, pp. 244–254

Abstract

True linear relationships are rare in clinical data. Despite this, linearity is often assumed during analyses, leading to potentially biased estimates and inaccurate conclusions. In this introductory paper, we aim to first describe-in a non-mathematical manner-how to identify non-linear relationships. Various methods are then discussed that can be applied to deal with non-linearity, including transformations, polynomials, splines and generalized additive models, along with their strengths and weaknesses. Finally, we illustrate the use of these methods with a practical example from nephrology, providing guidance on how to report the results from non-linear relationships.

Authors 6

1. Nicholas C Chesnaye corresponding

   Amsterdam UMC Location University of Amsterdam · Amsterdam Public Health

   Affiliation as printed

   Amsterdam Public Health Research Institute, Quality of Care , Amsterdam ,

   ERA Registry, Amsterdam UMC location University of Amsterdam, Medical Informatics , Amsterdam ,

   Amsterdam Public Health Research Institute, Quality of Care , Amsterdam , The Netherlands

   ERA Registry, Amsterdam UMC location University of Amsterdam, Medical Informatics, Meibergdreef 9, Amsterdam, The Netherlands

2. Merel van Diepen Aachen Department of Clinical Epidemiology

   Leiden University Medical Center

   Affiliation as printed

   Department of Clinical Epidemiology, Leiden University Medical Center , Leiden ,

   Department of Clinical Epidemiology, Leiden University Medical Center , Leiden , The Netherlands

3. Friedo Wilhelm Dekker Aachen Department of Clinical Epidemiology

   Leiden University Medical Center

   Affiliation as printed

   Department of Clinical Epidemiology, Leiden University Medical Center , Leiden ,

   Department of Clinical Epidemiology, Leiden University Medical Center , Leiden , The Netherlands

4. Carmine Zoccali
   Affiliation as printed

   Associazione Ipertensione Nefrologia Trapianto Renale (IPNET), c/o Nefrologia, Grande Ospedale Metropolitano , Reggio Calabria ,

   Associazione Ipertensione Nefrologia Trapianto Renale (IPNET), c/o Nefrologia, Grande Ospedale Metropolitano , Reggio Calabria , Italy

5. Kitty J. Jager

   Amsterdam UMC Location University of Amsterdam · Amsterdam Public Health

   Affiliation as printed

   Amsterdam Public Health Research Institute, Quality of Care , Amsterdam ,

   ERA Registry, Amsterdam UMC location University of Amsterdam, Medical Informatics , Amsterdam ,

   Amsterdam Public Health Research Institute, Quality of Care , Amsterdam , The Netherlands

   ERA Registry, Amsterdam UMC location University of Amsterdam, Medical Informatics, Meibergdreef 9, Amsterdam, The Netherlands

6. Vianda S Stel

   Amsterdam UMC Location University of Amsterdam · Amsterdam Public Health

   Affiliation as printed

   Amsterdam Public Health Research Institute, Quality of Care , Amsterdam ,

   ERA Registry, Amsterdam UMC location University of Amsterdam, Medical Informatics , Amsterdam ,

   Amsterdam Public Health Research Institute, Quality of Care , Amsterdam , The Netherlands

   ERA Registry, Amsterdam UMC location University of Amsterdam, Medical Informatics, Meibergdreef 9, Amsterdam, The Netherlands