# bayes theorem disease problem

• Nov 22nd 2010, 09:24 AM
eleahy
bayes theorem disease problem
A=event that the tested person has the disease
B= event that the test is positive
we know P(B/A)=.9 AND P(B/not A)=0.1
also 1% of population hs the disease
find p(A/B)

i know you use bayes formula here but I dont know how you get the value of p(A) to put in the formula!!the formula im using is [p(B/A)P(A)]/[P(B/A)P(A)+P(B/NOTA)P(NOTA)

I think I hae all values but p(a) and is the 1% of population used in answer??

got .0833 as an answer i used .01 as p(a)
• Nov 23rd 2010, 03:07 AM
CaptainBlack
Quote:

Originally Posted by eleahy
A=event that the tested person has the disease
B= event that the test is positive
we know P(B/A)=.9 AND P(B/not A)=0.1
also 1% of population hs the disease
find p(A/B)

i know you use bayes formula here but I dont know how you get the value of p(A) to put in the formula!!the formula im using is [p(B/A)P(A)]/[P(B/A)P(A)+P(B/NOTA)P(NOTA)

I think I hae all values but p(a) and is the 1% of population used in answer??

yes

Quote:

got .0833 as an answer i used .01 as p(a)
OK

CB