Probability notation

math boolean probability notation probability-theory
user1328370 picture user1328370 · Aug 31, 2012 · Viewed 11.3k times · Source

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 ?

Answer

Novak picture Novak · Aug 31, 2012

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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