Statistics, data and evidence · Methods and tools

When can a statistical correlation justify a claim about cause?

Everyone learns that correlation does not imply causation, yet many of our most important causal beliefs, such as that smoking causes cancer, rest largely on statistical association. This question asks what extra reasoning turns a correlation into knowledge of a cause.

Claims

When an association is strong, consistent across studies, follows the right time order and has a plausible mechanism, a causal conclusion is justified even without an experiment.
Statistical methods can adjust for other variables, which helps separate real causes from coincidences.

Counterclaims

A hidden third variable can always be suggested, so correlational evidence never gives the certainty of a controlled experiment.
Deciding that the evidence is 'enough' is a judgement that can be influenced by interests, as the history of tobacco research shows.

Real-life situations from mathematics

Smoking and lung cancer

In 1950 Richard Doll and Austin Bradford Hill published a study linking smoking with lung cancer. The statistician R. A. Fisher argued the link might come from a common genetic factor. In 1965 Bradford Hill set out considerations, such as strength and consistency, for judging when an association is likely to be causal.

Ice cream and drowning

Ice cream sales and drownings rise and fall together over a year, a standard example of two effects of a common cause: warm weather.

Check dates and figures in a reliable source before you use them, and cite that source.

Use this in your TOK work

Essay. Fits titles about evidence, causation and certainty in the human and natural sciences.

Exhibition. A scatter graph from a news article claiming one thing causes another is an easy object to analyse critically.

Link it to the prescribed title or the exhibition prompt you are working on, in your own words. See using maths examples in your essay and choosing exhibition objects.

Themes and study heading

Knowledge and the knower Methods and tools

How mathematical knowledge is produced and justified.