Monday, September 20, 2010

Things depend

xkcd comments on using unconditional probability in situations when what's relevant is conditional probability:


Happens all the time. How many times have you heard someone say "Sure, the probability of winning the lottery may be very small... but someone wins it nonetheless!" Or take a more ominous example: Alan Dershowitz's claim, made during O. J. Simpson's trial, that since less than 1 in a 1000 women abused by their partners are also killed by them, the fact that Simpson abused his wife doesn't make it much more likely that he killed her. Makes me wonder how many people were falsely convicted or acquitted because of erroneous arguments like this not having been exposed.

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