Cause test could end up in court

Proving the cause of something is notoriously difficult. A new test claims to be able to find such causes, and it might end up in the courtroom very quickly

JUST because two events happen together does not mean one caused the other. That inconvenient truth is drummed into every aspiring scientist (and science journalist) right at the start of their education. No matter how suggestive the correlation between two variables may be, it does not add up to proof of causation. That only comes with controlled experiments, and in real-world situations these are often impossible.

This distinction affords plenty of opportunity to obfuscate. For example, tobacco companies successfully argued for decades that the mass of evidence linking their product with cancer was merely correlational. Smoking could not be said to cause cancer, and thus there was no justification for, say, putting health warnings on packs of cigarettes. Experiments eventually proved the link existed - but not before many smokers had gone to an early death.

A new statistical test could cut through all that (see "Causality test could help preserve the natural world"). George Sugihara says his CCM test can identify connections that would otherwise remain obscure.

CCM is at an early stage, and already has its detractors. It clearly needs to be tested further before we can tell how robust its predictions are. But some people may not wait for such validation.

What if, for example, a causal link could be shown between some set of greenhouse gas emissions and a particular manifestation of climate change? Or within the complex interactions of banking and world economies?

These areas are already the subject of protests and litigation, frequently based on correlations and expert testimony. Lobbyists and lawyers are likely to seize upon a statistical test that can be used to back up their claims, even if its interpretation remains ambiguous, seeing it as a way to nail organisations that seem to have thus far evaded being called to account for their actions.

This idea is enticing but dangerous. Until the detailed ramifications of this test are well understood, using it to allocate blame risks a miscarriage of justice. For the law, as for science, the acid test should remain that something must be proved beyond reasonable doubt.

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