A new antibody test detects serum antibodies against virus X (sensitivity 99%, specificity 90%). When applied in a group of hospitalized patients diagnosed as having virus X infections, the test is found to have a positive predictive value of 85%. When used to screen a group of healthy blood donors for virus X infections, the test is found to have a positive predictive value of 30%. Which of the following best explains this difference between the positive predictive values?
| A. |
The prevalence of virus X infection is higher among the hospital patients than among blood donors |
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| B. |
Lead time bias occurs among the blood donors |
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| C. |
Measurement error was introduced into the procedure. |
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| D. |
Cases of virus X infection are more severe in the hospital |
The correct answer is option A. The prevalence of virus X infection is higher among hospital patients than among blood donors. Because in patient's virus concentration is high, allowing the drug to react more and showing more results, but in healthy patients, the virus is absent so the drug is not working at full capacity, showing minimal results.
A new antibody test detects serum antibodies against virus X (sensitivity 99%, specificity 90%). When applied...
3. The standard blood test screen for the Human Immunodeficiency Virus (HIV) detects antibodies to the virus using a laboratory test known as ELISA (enzyme-linked immunosorbent assay). If the ELISA test is run properly under recommended conditions, it has a sensitivity of 99% and a specificity of 99%. a) (4 pts) Assume the HIV-ELISA test is administered to a low-risk community of 100,000 people. By low-risk we mean a population which has an HIV prevalence of 1%. Construct the appropriate...
In this hypothetical case study, a new rapid test kit nicknamed Alpha is being reviewed. The sensitivity of Alpha is 93.0% (0.93) and the specificity is 96.0% (0.96). Assume that the actual prevalence of the Zika antibody among the United States population of blood donors is 4% (0.04) and that of the hurricane disaster relief volunteers returning from Puerto Rico is 20.0% (0.20). Construct a 2 x 2 table, to calculate the positive predictive value (PPV) and the negative predictive...