Confounding

"Confounding factor" redirects here. For the company, see Confounding Factor. For the psychological state, see Confusion.
Whereas a mediator is a factor in the causal chain (above), a confounder is a spurious factor incorrectly implying causation (bottom)

In causal inference, a confounder[a] is a variable that influences both the dependent variable and independent variable, causing a spurious association. Confounding is a causal concept, and as such, cannot be described in terms of correlations or associations.[1][2][3] The existence of confounders is an important quantitative explanation why correlation does not imply causation. Some notations are explicitly designed to identify the existence, possible existence, or non-existence of confounders in causal relationships between elements of a system.

Confounders are threats to internal validity.[4]


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  1. ^ Pearl, J., (2009). Simpson's Paradox, Confounding, and Collapsibility In Causality: Models, Reasoning and Inference (2nd ed.). New York : Cambridge University Press.
  2. ^ VanderWeele, T.J.; Shpitser, I. (2013). "On the definition of a confounder". Annals of Statistics. 41 (1): 196–220. arXiv:1304.0564. doi:10.1214/12-aos1058. PMC 4276366. PMID 25544784.
  3. ^ Greenland, S.; Robins, J. M.; Pearl, J. (1999). "Confounding and Collapsibility in Causal Inference". Statistical Science. 14 (1): 29–46. doi:10.1214/ss/1009211805.
  4. ^ Shadish, W. R.; Cook, T. D.; Campbell, D. T. (2002). Experimental and quasi-experimental designs for generalized causal inference. Boston, MA: Houghton-Mifflin.