another biostat ques- Please explain - lavender44

[ArchivalUser]

A new stool test for H.pylori infection yields infection yields positive results in 80% of infected pts and 10% of uninfected pts. Prevalence of H.pylori in the population is 10%. What is the probability that a pt who tests positive with the new test is infected with the H.pylori?
A-25%
B-33%
C-47%
D-54%
E-75%

[ArchivalUser]

http://www.usmleforum.com/showthread.php?tid=788898 take look @ my Q. same conc.

[ArchivalUser]

PPv : 47%

[ArchivalUser]

sens is 80 %
But what is spec ? how to get that?

[ArchivalUser]

cardio or zaika please help here

[ArchivalUser]

you need to arbitrary choose the size of the sample . I chose 100 , then I know 10% OF POP OF 100 is 10 and I fill the bottom line of the table, the rest followed with the data given