Porbability, not sure I get it

  • Context: Undergrad 
  • Thread starter Thread starter liquidFuzz
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Discussion Overview

The discussion revolves around the application of probability theory, specifically Bayes' theorem, in the context of string matching. Participants are trying to clarify the calculation of probabilities related to true hits and artifacts in string comparisons, while also addressing the clarity of the examples provided.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant presents a scenario involving the calculation of probabilities for true hits and artifacts in string matching, suggesting the use of Bayes' theorem.
  • Another participant expresses confusion about the initial examples and requests a general description of the problem.
  • Some participants clarify the definitions of probabilities A and B, with A representing the probability of an event occurring and B representing the probability of an error given that event.
  • Concerns are raised about the clarity of the source of the probabilities, with one participant noting that probability values above 1 are nonsensical.
  • A participant mentions that the text lacks context, making it difficult to understand the probabilities being discussed.

Areas of Agreement / Disagreement

Participants generally express confusion and seek clarification on the problem being discussed. There is no consensus on the definitions or calculations of the probabilities, and multiple viewpoints regarding the clarity of the examples remain unresolved.

Contextual Notes

Limitations include unclear definitions of the probabilities involved, the lack of context for the examples, and the potential for misunderstanding due to vague reasoning in the initial text.

liquidFuzz
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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]
 
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I don't get what you want to calculate.
Can you add a general description instead of 2 uncommented examples?
 
mfb said:
I don't get what you want to calculate.
Can you add a general description instead of 2 uncommented examples?
A = Probability of something happening
B = Probability of something goes wrong if A happened.
 
That is not the problem.
What do you want to calculate, where do those probabilities come from, and so on?

B = Probability of something goes wrong if A happened.
So P(B) is P(goes wrong|A)?
 
Ok, I snitched the text that got my puzzled. Please comment!
 

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Did you have a particular question in mind given your snitch?
 
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.
 
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?
 
I guess I'll get away with just commenting this. "Vague reasoning."

Thanks!
 

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