muxia wrote:
A Screening test for colon ca is adminitered to 1000 people with biopsy proven colon Ca and 1000 people without colon Ca. Test results are positive for 250 of the priven cases and 100 of these withour colon Ca. The screening test is now to be used on a populations od 100 000 people with a known prevalence rate of colon Ca os 80 per 100 000. Which of the foll. is the expected number of the true positives and false positive in n 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 60 89.928
G 80 9992
I 80 89.928
please, expl!!
how was form 4 for u? i found it tough.
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| medocuk
IM-RES
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I didn't get.Can some one please explain how they deduced these answeres.Ive been getting all these questions wrong. 
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| muxia
Forum Newbie
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Posts: 44
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Thanks to all...was useful...
All forms were tough for me  exam after tomorrow!!!
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| test123
Forum Newbie
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Posts: 16
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IN THE QUESTION IT SAYS 250 PROVEN CASES (True positives) IN 1000 PEOPLE WITH CARCINOMA=25%
100 False positive cases in 1000 people with out carcinoma = 10%.
The screening test is now to be used on a populations of 100 000 people with a known prevalence rate of colon Ca of 80 per 100 000.
That means out of 80 proven cases how many are true positive (which is 25%) =20
99,920 cases are non carcinoma cases(100,000-80 proven cases)
10% of 80 proven cases = 9920.
Answer is A.
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