FILE SELECTED // FILE 00
Conditional Probability
“A new condition changes the universe of cases you are counting over.”
01 / SUMMARY
In short
P(A|B) is the probability of A restricted to situations where B occurred, provided P(B) is positive. It usually differs from P(A) and is not interchangeable with P(B|A).
03 / SCENE
In the wild
The probability of rain given overcast skies is not the probability of overcast skies given rain.
04 / LIMIT
The limit
Reversing the condition is a common error, especially when interpreting diagnostic tests.
FINAL NOTE
What remains
Read the bar as given that and name the new reference universe first.