USMLE Forums banner
1 - 4 of 4 Posts

·
Registered
Joined
·
114 Posts
Discussion Starter · #1 ·
You are working with rare diseases. You have laboratory test which will confirm a disease that affects 1 in 100 000 in general population. Test have sensitivity of 99% and specificity of 95%. How many percent of those who have test positive in the end has the disease?.

a) 0,02%
b) 0,2%
c) 2%
d) 20%
 

·
Registered
Joined
·
1,357 Posts
You are working with rare diseases. You have laboratory test which will confirm a disease that affects 1 in 100 000 in general population. Test have sensitivity of 99% and specificity of 95%. How many percent of those who have test positive in the end has the disease?.

a) 0,02%
b) 0,2%
c) 2%
d) 20%
Prevalence = 1/100.000

Sensitivity = P(+|D) = 0.99
Specificity = P(-|D´) = 0.95

How many percent of those who have test positive in the end has the disease? = P(D|+) in %

So, 1 every 100.000 ==> 100 every 10.000.000

............D.........D´
test +...99....... 499995..... 500094
test -....1........xxxx
Total .100..... 9999900...10.000.000

D = Disease
D´= Disease free

P(D|+) = 99/500094 = 0.0002

in % = 0.0002*100 = 0.02%
 
1 - 4 of 4 Posts
Top