nbme form 1 block 4 q 40 - kiranraja

[ArchivalUser]

40. The genetic disease institute at a university hospital has developed a rapid screening test for a serious but treatable inherited metabolic disorder. Although this disorder is predominantly found in a particular ethnic group, it is also found sporadically throughout the entire population. The screening test has a sensitivity of 95% and a specificity of 90%. When used in an ethnically prescreened population where the prevalence of this disorder is 30%, the positive predictive value is 80% and the negative predictive value is 96%. The institute proposes to use this screening test on the general population where the prevalence of this disease is 0.1%. Which of the following is the most likely result of this screening program?

A
) Negative predictive value decreases

B
) Positive predictive value decreases

C
) Sensitivity decreases

D
) Specificity decreases

[ArchivalUser]

B..

[ArchivalUser]

B makes sense,
coz PPV is highly sensitive to prevalance. Higher the prevalance more is PPV and vice versa. So PPV will decrease if the same screening test will used in the population with 0.1% prevalance.

Sen and spe are never affected by prevalance.

[ArchivalUser]

bbb

[ArchivalUser]

BBB ... prevalence decreases and so PPV decreases