Jackofknives
Ipwnpoker.com
Topics: 91
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A new blood test to detect prostate cancer was given to 1000 male members of a large HMO. Although 50 of the men actually had prostate cancer, the test was positive in only 15; the other 35 pts with prostate cancer had negative tests. Of the 950 men without prostate cancer, the test was positive in 200 men and negative in 750. if the cutoff value indicating a positive test is lowered from 4 ng/ml to 3 ng/ml, with this change in the cutoff value, the incidence and prevalence of prostate cancer would
increase, increase
decrease, decrease
increase, not change
not change, not change
increase, decrease
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| robin082006
Forum Hero
Topics: 471
Posts: 5,123
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not change, not change
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| DRSVANITHA
Forum Newbie
Topics: 0
Posts: 2
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increase , increase
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| new_n_lost
Forum Hero
Topics: 673
Posts: 6,141
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increase, not change ???
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| po
Forum Elite
Topics: 39
Posts: 356
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robin082006 wrote:
not change, not change
Not sure about incidence though,agree with prevalence,
The Yin and the Yang of sensitivity and specificity: the benefit is that sensitivity and specificity are largely unaffected by the prevalence of disease. The detriment is that sensitivity and specificity are largely unaffected by the prevalence of disease and therefore will give you a false sense of security when the prevalence of disease is either very high (increased false negatives with highly sensitive tests) or very low (increased false positives with highly specific tests).
Some people have trouble with the concept of prevalence. It’s also called “pre-test likelihood”; in other words, prevalence is the likelihood that the patient has the disease. Knowing the prevalence is very important as one interprets test results.
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| junoon
Topics: 4
Posts: 47
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I think the incidence will not change but the prevalance would go upi-e increases b/c whenever the cut off value for a test being +ve is reduced or lowered more & more people will come is the diseased category.
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| kiterunner
Forum Junior
Topics: 14
Posts: 63
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Not change, Not change (in given situation)
Screening does not assess incidence, so incidence will not change.
Screening does assess prevalence, but prevalence (TP+FN/TP+FP+TN+FN) is not affected by raising or lowering cut off point, particularly when it`s already given out in the stem (TP+FN =50). Change of cut off point only affects Sensitivity, Specificity, PPD & NPD.
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| Jackofknives
Ipwnpoker.com
Topics: 91
Posts: 733
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Answer is 4
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