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			== Confounding ==
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'''Confounding''' is a concept in [[epidemiology]] that refers to a situation where the effect or association between an [[exposure]] and an [[outcome]] is distorted by the presence of another variable. The variable that causes this distortion is referred to as a confounding variable or a confounder.

==Definition==
Confounding occurs when the [[causal effect]] of one variable on the outcome is mixed with the effect of another variable on the outcome. The confounding variable is associated with both the exposure and the outcome, but is not on the causal pathway between the exposure and the outcome.

==Types of Confounding==
There are three main types of confounding:
* '''[[Positive confounding]]''' occurs when the observed association is biased away from the null.
* '''[[Negative confounding]]''' occurs when the observed association is biased towards the null.
* '''[[Partial confounding]]''' occurs when the observed association is biased, but not as much as in positive or negative confounding.

==Control of Confounding==
There are several methods to control for confounding, including:
* '''[[Randomization]]''' in the design of the study
* '''[[Stratification]]''' or '''[[matching]]''' in the analysis of the study
* '''[[Statistical adjustment]]''' in the analysis of the study

==Examples==
An example of confounding occurs in a study of the association between [[smoking]] and [[lung cancer]]. If age is also associated with lung cancer (older people are more likely to get lung cancer), and age is associated with smoking (older people are more likely to smoke), then age is a confounder in the study. If not controlled for, the effect of smoking on lung cancer may be overestimated.

==See Also==
* [[Bias (epidemiology)]]
* [[Causal inference]]
* [[Epidemiology]]
* [[Observational study]]
* [[Randomized controlled trial]]

[[Category:Epidemiology]]
[[Category:Statistical terminology]]
[[Category:Medical terminology]]
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Confounding - Revision history

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