Confounding factor

In statistics, a confounding factor, often simply called a confounder, is a factor which is the common cause of two things that may falsely appear to be in a causal relationship. It is the cause of a spurious relationship. In statistical experimental design, attempts are made to remove confounding factors from the experiment.

For example, ice cream consumption and murder rates are highly correlated. Now, does ice cream incite murder or does murder increase the demand for ice cream? Neither: they are joint effects of a common cause or confounding factor, namely, hot weather.

An experiment that fails to take a confounding variable into account is said to have poor internal validity.

See also

• Spurious relationship
• Joint effect