Conditional probabilitys Flashcards
What is the multipication rule
Pr (A and B) = Pr(A) * Pr(B|A) = Pr(B)*(A|B)
What is the adition rule
Pr(A orB) = Pr(A) +Pr(B) - Pr(A and B)
Define the difference between mutually exculsive and independant events
Independant events is when one event has no effect on a second event
Mutually exlusive events CANNOT possibly both happen as they have no intersection
What is an intersection between two groups
When there is a cross over between two sample spaces,
eg
Being both right handed and female
Define what complementary ‘ness’ is
A is the probability of an event happening
A- (complement) is the probability A will not happen, 1-A=A-
How can we check if events are independant
Pr (B) = Pr(B|A)
What are the two rules of Tree diagrams
Multiply along branches - Multiplication rule
Add down branches - Unition rule
Dependant events will be conditional on the previous branch
What is a diagnostic tests purpouse
To determine how accurate a test determined by two factors is
- often whether you have a disease and did the test return postive
What is the definition of specificity and sensitivity
A = having a condition
B = a postive test
Assume:
Specificity: (-B|-A)
- ensure you dont get postive given not having condition
Sensitivity: Pr (B|A)
Define postive prediction and negative prediction probabilitys
Assume:
A = having a condition
B = a postive test
postive prediction: Pr(A|B)
negative prediction: Pr(-A|-B)
How to calculate the probability of B Pr(B)
Pr(A and B) + Pr(A- and B)
How to calculate Pr(A|B)
Pr(A and B)/Pr(B)
