Talk:Conditional probability

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I've struck out the sentence about decision trees. There is certainly no sense in which conditional probability calculations are generally easier with decision trees. Decision trees can indeed be interpreted as conditional probability models (or not), but in any event, they are a very, very small part of the world of conditional probability, and making an unwarranted assertion about a minor topic is out of place. Wile E. Heresiarch 17:13, 1 Feb 2004 (UTC)

[edit] Wrong?

Conditional probability is the probability of some event A, given that some other event, B, has already occurred

...

In these definitions, note that there need not be a causal or temporal relation between A and B. A may precede B, or vice versa, or they may happen at the same time.

This statement is totally confusing - if event B has already occurred, there has to be a temporal relation between A and B (i.e. B happens before A). --Abdull 12:50, 25 February 2006 (UTC)

I've reworded it. --Zundark 14:32, 25 February 2006 (UTC)
Great, thank you! --Abdull 11:24, 26 February 2006 (UTC)


[edit] Undefined or Indeterminate?

In the Other Considerations section, the statement If P(B) = 0, then P(A \mid B) is left undefined. seems incorrect. Is it not more correct to say that P(A \mid B) is indeterminate?

If P(B) = 0, then P(A \cap B) = 0 regardless of P(A) or P(A \mid B).

Bob Badour 04:36, 11 June 2006 (UTC)

It's undefined. If you think it's not undefined, then what do you think its definition is? --Zundark 08:54, 11 June 2006 (UTC)
Indeterminate as I said, the definition of which one would paraphrase to incalcuable or unknown. However, an indeterminate form can be undefined, and the consensus in the literature is to call the conditional undefined in the abovementioned case. There are probably reasons for treating it as undefined that I am unaware of, and changing the text in the article would be OR. Thank you for your comments, and I apologize for taking your time. -- Bob Badour 00:07, 12 June 2006 (UTC)

[edit] Use of 'modulus signs' and set theory

Are the modulus signs in the "Definition" section intended to refer to the cardinality of the respective sets? It's not clear from the current content of the page. I think the set theory background to probability is a little tricky, so perhaps more explanation could go into this section?

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