Example involving conditional probability and transitivity

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Discussion Overview

The discussion revolves around understanding conditional probability, specifically the manipulation of expressions involving conditional probabilities and the application of the law of total probability. Participants are exploring how to rewrite certain probability expressions and the reasoning behind those manipulations.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant seeks clarification on how to rewrite P(T|A) as a sum of products of conditional probabilities.
  • Another participant asserts that the manipulation is based on a general statement about probabilities, not specifically tied to conditional probabilities.
  • A participant expresses confusion about the relationship between P(T|A) and the expression P(T|A,F), questioning the source of P(T|A,F)*P(F|A).
  • There is a mention of the law of total probability for conditional probabilities as a potential solution to the manipulation issue.
  • One participant questions the notation P(T|A,F) and its consistency with previously provided notation.
  • A later reply indicates that the notation was an attempt to simplify the discussion but suggests it should be disregarded.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of conditional probabilities in the manipulation process, and there is no consensus on the notation used or the specific steps to arrive at the desired expressions.

Contextual Notes

There are unresolved questions regarding the assumptions behind the manipulations and the definitions of the notation used, particularly concerning the relationship between different conditional probabilities.

hodor
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I'm just going to post a screenshot of the Example (free online textbook). I'm having a tough time making the leap to the first sum - what allows me to rewrite P(T|A) as the sum of the product of those two conditional probabilities?

x0YhzYJ.png


Thanks
 
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It doesn't have anything to do with the fact that you have a conditional probability to start, it's an application of the more general statement
[tex]P(X=true) = P(X=true | Y = true)P(Y= true) + P(X = true | Y = false)P(Y = false)[/tex]
 
Well I understand the bolded statement. I don't know why it doesn't have anything to do with the fact that I'm dealing with a conditional probability, since it's P( T = tr | A = tr ). In my mind I'm looking for an algebraic substitution or something that I know that allows me to manipulate this into something resembling P(T|A,F). What I don't know is where the P(T|A,F)*P(F|A) comes from or how I could get there.

For example, why not P(T|F,A)*P(F) and sum over F? Why is it P(F|A)?
 
Ok, I found what I was looking for. It's an application of the law of total probability for conditional probabilities:

8UvY6P4.png
 
hodor said:
something that I know that allows me to manipulate this into something resembling P(T|A,F). What I don't know is where the P(T|A,F)*P(F|A) comes from or how I could get there.

What is the notation "P(T|A,F)" supposed to mean? It isn't consistent with the notation in the image you gave.
 
Just an attempt to shorthand what was in the image since I'm on my phone. That post should just be ignored at this point.
 

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