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Post by Admin on Jan 17, 2016 20:04:33 GMT
β-Thalassemia major results from a homozygous genotype that leads to complete absence of both of the β-globin chains. A study subjected 100,000 participants to an intrauterine screening test; 87 tested positive for β-thalassemia major, and the remaining 99,913 tested negative. In 7 of those 87 cases the results were shown to be false positive. Ultimately, 100 of those originally screened were found to actually have the disease.
Which of the following is the correct sensitivity of the intrauterine screening test?
A. 8%
B. 80%
C. 87%
D. 92%
E. 99.99%
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Post by Admin on Jan 17, 2016 20:05:11 GMT
If 7 of 87 subjects who tested positive actually did not have β-thalassemia, then we know that 80 had true-positive results. One hundred of the original sample actually had the disease. Sensitivity is the proportion of people with a disease who test positive divided by the number of people with that disease. The screening test results were positive in 80 of the 100 patients with β-thalassemia. Therefore, sensitivity = 80/100 = 80%, as shown in the image.
A is not correct. 5% chose this.
This answer represents a calculation error.
C is not correct. 19% chose this.
The answer 87% would be the result had 7 false positives not been recognized.
D is not correct. 16% chose this.
Positive predictive value = 80/87 = 92%.
E is not correct. 7% chose this.
Specificity = 99,893/99,900 = 99.99%.
Bottom Line:
Sensitivity is measured by the proportion of people with a disease who test positive divided by the number of people with that disease.
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