Incorrect comments on Help me teach Bayes’

Incorrect 11 Apr 2012 18:27 UTC
3 points
```
P(A and B) = P(B and A)
P(A and B) = P(A) * P(B|A)
```
=>
```
P(A and B) = P(A) * P(B|A)
P(B and A) = P(A) * P(B|A)
P(B) * P(A|B) = P(A) * P(B|A)
P(A|B) = P(A) * P(B|A) / P(B)
```
- XiXiDu 11 Apr 2012 19:13 UTC
  0 points
  Parent
  
  P(B and A) = P(A) * P(B|A)
  
  To make it clearer, shouldn’t this step be = P(B) * P(A|B)?
  
  Also, are middle school pupil in the U.S. familiar with the notation? Maybe one should state it in English instead?
  
  The probability of A if B is known to occur is equal to the probability of A times the probability of B if A is known to occur divided by the probability of B.
  
  ETA
  
  P(A and B) = P(A) * P(B|A)
  
  The probability of A and B to occur at the same time is the same as the probability of A to occur alone times the probability of B to occur under the condition that A is known to occur.
- A1987dM 11 Apr 2012 19:06 UTC
  −2 points
  Parent
  Spot the typo.
  - Incorrect 11 Apr 2012 19:28 UTC
    0 points
    Parent
    Don’t see one. Could you please tell me where?
    - A1987dM 11 Apr 2012 19:34 UTC
      0 points
      Parent
      I think the second line after the ⇒ was supposed to be P(B and A) = P(B) * P(A|B).
      - Incorrect 11 Apr 2012 19:52 UTC
        1 point
        Parent
        No, it’s a substitution on the left hand side. I substituted P(A and B) for P(B and A)