Biostat Q - conquerstep3

[ArchivalUser]

Stool test for H.pylori infection gets positive result in 80% of infected pt.'s and in 10% of uninfected pt.'s.
Prevalence of H.Pylori infection in population is 10%.
What is the probability that a pt. who tests positive withe the new test is infected with H.Pylori?

[ArchivalUser]

hey conquerstep3 it seems that you have just recently written the exam? rt
the answer is 88.88(may have options like 88 or 89). hope it's the rt answer.
good luck

[ArchivalUser]

Or 80/90

[ArchivalUser]

I haven't taken the exam yet...but thanks for the wishes saad182

I will post answer tomorow, will give some time,if others want to answer

[ArchivalUser]

answer is 47%

[ArchivalUser]

Why? Isn't it asking for ppv= TP/TP+FP:80/90

[ArchivalUser]

it is asking for PPV

but you have to take in account Prevalence, which is 10%

[ArchivalUser]

TP= sensitivity x prevalence

FP=(1-specificity) X (1-prevalence)

[ArchivalUser]

Can you please write the calculations?

[ArchivalUser]

yes 47%