Statistics again

Ken writes: Further to Dot’s earlier post on the subject of statistics, Language Log has an interesting and informative post on ‘the base rate fallacy’. This fallacy, in brief, is to reason that if you get a positive result from a test that is 99% accurate, there’s a 99% chance you have the condition it was testing for. This is fallacious because you are ignoring the background incidence (the base rate) of the condition in the population. If a condition is extremely rare, then, even if you have a positive result from an accurate test, you are still not likely to have it.

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