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Prep4USMLE Forum » USMLE Step 2 CK Forum » Preventive Medicine

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5 Posts

sweetybokhari
Forum Elite

Topics: 118
Posts: 148

03/17/07 - 11:01 AM

Hemochromatosis has a prevalence of 0.5% in the general population.the treatment of choice is regular phlebotomy.you have decided to initiate a new test for this disease.the literature indicates a sensitivity of 80.5% and a specificity of 89.5% for this test.you decide to screen 1000 people and institue treatment solely on the results of the test.which one of the following is correct?
1) you will treat 40 people with phlebotomy
2) 995 people will not be treated
3) 100 people who do not have the disease will be treated with phlebotomy
4) 80% of the subjects will be correctly diagnosed
5) 200 people who have the disease will be denied treatment

new_n_lost
Politically InCorrect
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Topics: 654
Posts: 6,112

03/17/07 - 11:06 AM

2) 995 people will not be treated
I think
??

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robin082006
Forum Hero
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Topics: 471
Posts: 5,125

03/17/07 - 11:25 AM

3) 100 people who do not have the disease will be treated with phlebotomy (exact number is 105)

........... .disease------------not disease...........total

positive.....80.5*5=4----------995-890=105-------109

Negative.....1.........................995*89.5=890---891

Total........5............................995................1000

1) you will treat 40 people with phlebotomy: not relevant

2) 995 people will not be treated: incorrect

3) 100 people who do not have the disease will be treated with phlebotomy: possible, 105

4) 80% of the subjects will be correctly diagnosed: this says about PPV, the PPV for this test is very low

5) 200 people who have the disease will be denied treatment: not relevant

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92306
Forum Senior

Topics: 14
Posts: 126

03/20/07 - 01:45 PM

Very good explanation Robin.

sweetybokhari
Forum Elite

Topics: 118
Posts: 148

03/25/07 - 02:43 PM

thanks Robin ,good explanation.

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