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Self-fulfilling correlations

103 PhilGoetz 26 August 2010 09:07PM

Correlation does not imply causation.  Sometimes corr(X,Y) means X=>Y; sometimes it means Y=>X; sometimes it means W=>X, W=>Y.  And sometimes it's an artifact of people's beliefs about corr(X, Y).  With intelligent agents, perceived causation causes correlation.

Volvos are believed by many people to be safe.  Volvo has an excellent record of being concerned with safety; they introduced 3-point seat belts, crumple zones, laminated windshields, and safety cages, among other things.  But how would you evaluate the claim that Volvos are safer than other cars?

Presumably, you'd look at the accident rate for Volvos compared to the accident rate for similar cars driven by a similar demographic, as reflected, for instance in insurance rates.  (My google-fu did not find accident rates posted on the internet, but insurance rates don't come out especially pro-Volvo.)  But suppose the results showed that Volvos had only 3/4 as many accidents as similar cars driven by similar people.  Would that prove Volvos are safer?

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