No. 257 · Evidence · Statistics and Probability
Confounding Factor
When two things move together, a hidden third factor may be pulling both strings.
In the Almanac
“Ice cream and polio”, 1940s · “BJ’s Wholesale Club”, 2019
Both stories in full, three ways to use it and where it misleads.
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Questions
What is Confounding Factor?
A confounding factor is a hidden variable that influences both the supposed cause and the supposed effect, making them look connected when they may not be. Summer drove both polio cases and ice cream sales.
How do you use Confounding Factor?
To use it, ask what else changed when a result appears, check whether the people being compared started out alike, and trust randomised comparisons over simple before-and-after stories.
When does Confounding Factor matter?
Confounding Factor is one of the 68 mental models for evidence, the situations where you ask: Is this really true? Within that, it belongs to “Cause or coincidence?”, alongside Causal Fallacy, Clustering Illusion and Correlation and Causation.
What is an example of Confounding Factor?
Two stories show it at work: Ice cream and polio (1940s) and BJ’s Wholesale Club (2019). Both are told in full in The Mental Models Daily Almanac, which has two stories for each of its 365 models.
Which mental models are related to Confounding Factor?
Correlation and Causation, Causal Fallacy and Selection Bias. Confounding Factor itself comes from statistics and probability.