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I want to ask you about the notation in probability.

I know that

P(A | B) = the conditional probability that event A occurs given that event B has occurred already

But I cannot find what A,B or in my case P(A|B,C). I suggest it means "the conditional probability that event A occurs given that B and C BOTH occurred already"

I don't know what the comma means.

Can you help me ?

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closed as off topic by Jan Dvorak, jadarnel27, Rory McCrossan, Mahmoud Gamal, wtsang02 Feb 14 '13 at 14:46


Better asked on Mathematics –  AakashM Aug 31 '12 at 11:43

2 Answers 2

up vote 2 down vote accepted

You are basically correct.

P(A|B) is the probability of A given B. P(A|B,C) is the probability of A given (B and C).

You could just as easily write it as P(A|B^C) but it is notational convention to use a comma. Think of everything after the vertical bar as a list of the given things, separated by commas.

(And note that the vertical bar is a very high precedence operator, so to speak.)

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And is there a notation for "the probability of B or C, givven that A happened": P(A|[B or C]), not P(A,[B and C]) - just curious –  user1328370 Apr 23 at 14:29

This is according to Bayes rule

P(C|A,B) = P(A,B|C).P(C) / P(A,B)

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