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Old 08-05-2012
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Default What is the specificity of the test?

Researchers are assessing the specificity of a screening procedure for breast cancer in a population of 3000
women whose mothers had the disease. The presence or absence of a malignant condition is established by
conventional mammography, which is assumed to be definitive for the purposes of comparison. The following data
are collected:What is the specificity of the test?

...............Positive.. Negative..... Total
Cancer......90..............10...........100
No cancer...360..........2540.........2900
Total..........450..........2550........3000



A. 90/100

B. 90/450

C. 2540/2550

D. 2540/2900

E. (90+2540)/3000
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Quote:
Originally Posted by Novobiocin View Post
Researchers are assessing the specificity of a screening procedure for breast cancer in a population of 3000
women whose mothers had the disease. The presence or absence of a malignant condition is established by
conventional mammography, which is assumed to be definitive for the purposes of comparison. The following data
are collected:What is the specificity of the test?

...............Positive.. Negative..... Total
Cancer......90..............10...........100
No cancer...360..........2540.........2900
Total..........450..........2550........3000



A. 90/100

B. 90/450

C. 2540/2550

D. 2540/2900

E. (90+2540)/3000
D..............................
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Old 08-05-2012
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Explanation:

The correct answer is D. Specificity refers to how well a test identifies persons who do not have the disease in
question. In the example, 2900 women do not have breast cancer, and 2540 of these women have a negative
test. Specificity is given by (true negatives)/ (true negatives + false positives) = 2540/(2540+360) = 2540/2900.

Choice A, 90/100, represents the sensitivity of the test; that is, the proportion of women with the condition who
test positive.

Choice B, 90/450, gives the predictive value of a positive test. Of the 450 women who tested positive, 90 actually
had the condition.

Choice C, 2540/2550, gives the predictive value of a negative test. Of the 2550 who tested negative, 2540 did
not have cancer.

Choice E, (90+2540)/3000, refers to the efficiency of a test; that is, the proportion of all subjects who were
correctly classified by the test.
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