What is the difference between predictive value positive and sensitivity

Philadelphia, WB Saunders, , p. Minimizing false positives is important when the costs or risks of followup therapy are high and the disease itself is not life-threatening What is a good test in a population? Actually, all tests have advantages and disadvantages, such that no test is perfect. There is no free lunch in disease screening and early detection.

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Close Save changes. If the release is going to discuss potential unproven benefits, it should also mention the potential harms of screening tests including false- positives, false-negatives leading to over- or under-diagnosis. Chief among these harms would be falsely labeling healthy people as possibly having cancer and then subjecting them to invasive testing or even treatments that turn out to be unnecessary.

Both the news release and the news story would have been improved with discussion of two important concepts in medical testing: sensitivity and specificity. They are the yin and yang of the testing world and convey critical information about what a test can and cannot tell us.

The following graphic shows how these terms apply to one of the most commonly used tests: a pregnancy test. Increased sensitivity — the ability to correctly identify people who have the disease — usually comes at the expense of reduced specificity meaning more false-positives.

Airport security offers a good example how these tradeoffs play out in practice. To ensure that truly dangerous items like weapons cannot be brought on board an aircraft, scanners at a security checkpoint may also alarm for harmless items like belt buckles, watches, and jewelry. The scanner prioritizes sensitivity and will flag almost anything that seems like it could be dangerous. But that means it also has low specificity and is prone to false alarms; a positive result is much more likely to be a shampoo bottle than it is an explosive device.

The same issues crop up when it comes to testing for deadly diseases like cancer. High sensitivity is desirable: missing cases of actual cancer could lead to delays in treatment that negatively affect outcomes.

However, specificity is more important with cancer testing than it is at an airport checkpoint: false-positive results create anxiety and lead to unnecessary and invasive follow-up tests like biopsies.

They raise costs for everyone involved and increase the likelihood of experiencing harm. Those harms can be significant enough to outweigh the potential benefits of the test. Prostate specific antigen [PSA] testing is a good example low specificity test that generates many false-positive results.

Negative predictive value: If a test subject has a negative screening test, what is the probability that the subject really does not have the disease? In the same example, there were 63, subjects whose screening test was negative, and 63, of these were, in fact, free of disease. Interpretation: Among those who had a negative screening test, the probability of being disease-free was This widget will compute sensitivity, specificity, and positive and negative predictive value for you.

Just enter the results of a screening evaluation into the turquoise cells. In the video below, he discusses predictive value. All Rights Reserved. Date last modified: July 5, Wayne W. Screening for Disease.