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Old 11-09-2010
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Stats The percentage of test positive and have the disease?

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%
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Old 08-25-2011
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I think the answer is a) 0.02%
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Old 08-25-2011
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Quote:
Originally Posted by bebix View Post
I think the answer is a) 0.02%
can u explain it please??
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Old 08-25-2011
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Quote:
Originally Posted by fin-84 View Post
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(-|Dī) = 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.........Dī
test +...99....... 499995..... 500094
test -....1........xxxx
Total .100..... 9999900...10.000.000

D = Disease
Dī= Disease free

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

in % = 0.0002*100 = 0.02%
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The above post was thanked by:
drfchakera (08-27-2011), pass7 (08-30-2011)



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Biostatistics-Epidemiology, Step-1-Questions

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