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Porbability, not sure I get it

  1. Dec 19, 2012 #1
    An example of what I try to calculate. In a string matching between two strings the whole strings aren't compared, just a section.

    A = The probability of a true hit.
    A true hit being:
    PHP:
    |adcbacdcbacd|abacd
    |adcbacdcbacd|ab
    B = The probability of artifact being correct.
    Falls artifact being:
    PHP:
    |adcbacdcbacd|abacd
    |adcbacdcbacd|bca
    I though I'd use Bayes theorem to calculate the probability, but I'm not sure of how to do it.
    [itex]P(A|B)\frac{P(B|A)P(A)}{P(B)}[/itex]

    In my example A is much higher than B, would this imply:
    [itex]P(A|B)\frac{P(≈A)P(A)}{P(B)} ≈ P(A)[/itex]
     
  2. jcsd
  3. Dec 19, 2012 #2

    mfb

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    Staff: Mentor

    I don't get what you want to calculate.
    Can you add a general description instead of 2 uncommented examples?
     
  4. Dec 19, 2012 #3
    A = Probability of something happening
    B = Probability of something goes wrong if A happened.
     
  5. Dec 19, 2012 #4

    mfb

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    Staff: Mentor

    That is not the problem.
    What do you want to calculate, where do those probabilities come from, and so on?

    So P(B) is P(goes wrong|A)?
     
  6. Dec 22, 2012 #5
    Ok, I snitched the text that got my puzzled. Please comment!
     

    Attached Files:

  7. Dec 22, 2012 #6

    chiro

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    Science Advisor

    Did you have a particular question in mind given your snitch?
     
  8. Dec 22, 2012 #7
    Yeah, I don't quite get the part when he or she goes all P(A|B) and P(B|A).

    This is a part of a report that I'm helping to proofread.
     
  9. Dec 22, 2012 #8

    mfb

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    Probability values above 1 do not make sense. In addition, the text does not state clearly where probabilities come from. It is like "probability of an apple" - sure, I know apples, but an apple where, in which setup?
     
  10. Dec 22, 2012 #9
    I guess I'll get away with just commenting this. "Vague reasoning."

    Thanks!
     
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