NBME Form 4 ?

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NBME Form 4 ?

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pearljam59
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03/28/06 - 08:53 AM

17. A screening test for colon cancer is administered to 1O0O people with biopsy-proven colon cancer and to 10O0 people without colon cancer. The test results are positive for 250 of the proven cases and 100 of those without colon cancer. The screening test is now to be used on a population of 100,000 people with a known prevalence rate of colon cancer of 80 per 100,000 Which of the following is the expected number of true positives and false positives in this population of 100,000 people?

True Positive----False Positive
A) 20----------------9992
B) 20----------------89,928
C) 40----------------9992
D) 50----------------89,928
E) 60----------------9992
F) 80----------------89,928
G) 80----------------9992
H) 80----------------89,928

robin082006
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03/28/06 - 09:30 AM

Sensitivity= 20%

Answer is A

Specificity=90%

True Positive = Sensitivity*number of disease=25%*80=20

False positive = number of those without disease - true negative= (100 000 - 80) - (specificity*number of people without disease) = 99920 - 90%*99920 =9992

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tolito
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04/02/06 - 02:42 PM

A.

robin, sensitivity is 25%.

sens= TP DIV (TP+FN)
= 250/1000
=25%.

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robin082006
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04/02/06 - 03:45 PM

yes, typing error, thanks

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pearljam59
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04/07/06 - 08:55 AM

I am not following...where did you get Specificity from?!

shocked

tolito
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04/07/06 - 10:07 AM

from the negative guys, out of 1000, 100 were false positive. true neg is 900. specificity =900/1000=90%

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surgeon99
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04/20/06 - 08:51 AM

Disease No Disease Total
20 9992
60 89928
80 99920 100,000

vanshita
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04/24/06 - 05:34 PM

specificity 90

sensitivity 25

sensitivity= true+ve

sensitivity= true+ve

true+ve+false_ve

25%=true+ve

80

=20

false+ve=total-true_ve

100000-80=99920

humpf!!
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Topics: 51
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05/18/06 - 03:49 PM

Can we revisit this? i totally understood up to how you got senitivity and specificity...but what's all that after that?

robin082006 wrote:
Sensitivity= 25%

Answer is A

Specificity=90%

True Positive = Sensitivity*number of disease=25%*80=20

False positive = number of those without disease - true negative= (100 000 - 80) - (specificity*number of people without disease) = 99920 - 90%*99920 =9992

bd2005
Forum Newbie

Topics: 7
Posts: 24

05/19/06 - 10:10 AM

#10

Hi

You can solve it like this:

Attached Files:
Solving the statistic questions.mht (10 KB, 72 downloads)

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netlover
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Topics: 3
Posts: 54

05/28/06 - 01:32 PM

#11

bd2005 wrote:
Hi

You can solve it like this:

Good job, bd2005. I can't agree with you more

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