A 42 year old asymptomatic man with no past medical, family, or surgical history presents to you for a well adult visit. He takes no medications and has no allergies. He recently read about a new blood test for colon cancer called ColonFree. He wants to know if he should get this new blood test. You read an article about this new test for colon cancer. The value of this test in predicting colon cancer after a 10 year follow-up for a population of 1,000 asymptomatic men over age 50 is shown in the table below. Asymptomatic is defined as no gastrointestinal complaints, bowel movement changes, hematochezia, melena, or unexplained weight loss:
|Table: ColonFree blood test for colon cancer|
|Number of asymptomatic men (>50 age) that have colon cancer||Number of asymptomatic men (>50 age) that do NOT have colon cancer|
|Positive blood test||50||20|
|Negative blood test||30||900|
Which statement below is most accurate with regard to the usefulness of this new blood test for colon cancer?
|True Positive (TP)||False Positive (FP)||Positive Predictive Value = TP/(TP + FP)|
|False Negative (FN)||True Negative (TN)||Negative Predictive Value = TN/(TN + FN)|
|Sensitivity = TP/(TP+FN)||Specificity = TN/(FP+TN)|
The probability of the test finding disease among those who have the disease. Alternatively, the proportion of people with disease who have a positive test result.
The probability of the test finding no disease among those who do not have the disease. Alternatively, the proportion of people free of a disease who have a negative test.
Positive Predictive Value (PPV)
The percentage of people with a positive test result who actually have the disease. This is also the posttest probability that an individual has a disease after a positive test.
Negative Predictive Value (NPV)
The percentage of people with a negative test who do NOT have the disease. This is also the posttest probability that someone does not have a disease after a negative test.
The degree to which a consistent measurement is yielded by repeated applications of a test. A test is reliable if the average measurement error is small over time.
The degree to which a test actually measures what it claims to measure.
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