What Is a Confounder?
Looking for the full method? Read the detailed guide: What Are Confounding Variables?.
A confounder is a variable that is related to both the exposure (or treatment) and the outcome and is not on the causal pathway between them. If it is not accounted for, it can create or hide an apparent association.
Example
Invented for teaching: In a study of coffee and heart disease, smoking may confound the association if coffee drinkers smoke more and smoking raises heart disease risk. Adjusting for smoking helps separate the effects.
Common misunderstanding
Adjusting statistically does not remove all confounding, particularly if the confounder was not measured or was measured poorly. Randomisation balances confounders on average, which is why trials are strong for causal questions.
Learn more
Read What Are Confounding Variables?
References and further reading
- Hulley SB, Cummings SR, Browner WS, Grady D, Newman TB. Designing Clinical Research. 4th ed. Lippincott Williams & Wilkins; 2013. Link
- von Elm E, Altman DG, Egger M, et al. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. BMJ. 2007;335:806-808. doi:10.1136/bmj.39335.541782.AD
Related reading
This page is general educational information about research methods. It is not medical, legal or regulatory advice; follow your institution's ethics board and your target journal's instructions.