Base Rates

4 pages on this site touch on this topic.

• Base rates: how common is this, really? — The most under-used number in any coincidence story is how often the 'surprising' thing happens anyway, to someone, without any special explanation.
• Base-Rate Updater — See how a rare claimed ability, a good-sounding test, and a low base rate combine — most people who pass such a test still don't have the ability.
• Conditional probability: given what, exactly? — "How likely is A?" and "how likely is A, given B?" can have very different answers — and coincidence stories often quietly swap one for the other.
• Regression to the mean: extremes don't repeat — An unusually good or bad result tends to be followed by a more average one, for purely statistical reasons that have nothing to do with cause and effect.