藏经阁-How Bayesian inference works.pdf

Conditionalprobabilities

Conditionalprobabilitiesanswerthequestion“IfIknowthatapersonisawoman,whatistheprobabilitythatshehaslong

hair?”Conditionalprobabilitiesarecalculatedthesamewayasstraightprobabilities,buttheyjustlookatasubsetofallthe

examplesthosemeetingacertaincondition.Inthiscase,P(longhair|woman),theconditionalprobabilitythatsomeone

haslonghair,giventhatsheisawoman,isthenumberofwomenwithlonghair,dividedbythetotalnumberofwomen.This

turnsouttobe.5,whetherweareconsideringthemen’srestroomline,orthetheateroverall.