What are the 4 possible results of diagnostic testing?
1. True positive: Test + & disease + 2. True negative: Test - & disease - 3. False positive: Test + & disease - 4. False negative: Test - & disease +
A diagnostic test has a sensitivity of 80%, a specificity of 90%, a PPV of 60%, and an NPV of 95%. Your patient's test result comes back negative. What is the probability that they do not have the disease?
95%. This is the NPV, the probability of not having disease after testing negative.
A diagnostic test has a sensitivity of 80%, a specificity of 90%, a PPV of 60%, and an NPV of 95%. What is the probability that your patient will test positive if he has the disease?
80%. This is the sensitivity, the probability of a positive test result in patient with disease.
A diagnostic test has a sensitivity of 80%, a specificity of 90%, a PPV of 60%, and an NPV of 95%. What is the probability that your patient will test negative if he doesn't have the disease?
90%. This is the specificity, the probability of a negative test result in the absence of disease.
A diagnostic test has a sensitivity of 80%, a specificity of 90%, a PPV of 60%, and an NPV of 95%. What is the probability that your patient will test positive if he has the disease?
60%. This is the PPV, the probability of having disease after testing positive.
This brief visual tutorial is intended to provide an intuitive understanding of diagnostic test sensitivity, specificity, positive predictive value and negative predictive value. Make sure to cement your knowledge of this difficult material by answering the 5 quiz questions! For more evidence based medicine learning, check out this comic.