Correlation, Causation, and Confounders

One of the most important reasoning skills tested in the UCAT Decision Making subtest is the ability to distinguish between correlation (two things occurring together) and causation (one thing causing another). Many UCAT questions present data showing a statistical association and ask whether a causal claim is justified. This lesson teaches you to identify confounders, evaluate causal claims, and recognise common logical errors in data-based arguments.

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Correlation vs Causation

Correlation

Two variables are correlated when they tend to change together. This can be:

Type	Description	Example
Positive correlation	As one increases, the other increases	Ice cream sales and sunburn rates
Negative correlation	As one increases, the other decreases	Exercise frequency and body fat percentage
No correlation	No consistent relationship	Shoe size and exam results

Causation

Causation means one variable directly brings about a change in another.

"Smoking causes lung cancer" — there is a direct biological mechanism by which smoking damages lung tissue and leads to cancer.

The Critical Distinction

Correlation does not imply causation.