What term defines the probability that a patient has the condition after a test is applied?

What term defines the probability that a patient has the condition after a test is applied?

• A. Pretest probability
• B. Positive predictive value
• C. Negative predictive value
• D. Posttest probability

Answer: (D)

The key idea is updating your estimate of how likely the disease is after you see the test result. Posttest probability is the probability the patient has the condition once the test result is known, i.e., the posterior probability you get after applying the test. It comes from taking the pretest probability (your initial estimate) and adjusting it using the test’s performance (sensitivity and specificity) via Bayes’ theorem. Think of it this way: the pretest probability is where you started before testing. If the test is positive, you move to a higher posttest probability of disease (P(Disease | positive)); if the test is negative, you move to a different posttest probability (P(Disease | negative)). Positive predictive value and negative predictive value are specific posttest probabilities conditioned on the test outcome, but the general term for the updated probability after testing is posttest probability.

The key idea is updating your estimate of how likely the disease is after you see the test result. Posttest probability is the probability the patient has the condition once the test result is known, i.e., the posterior probability you get after applying the test. It comes from taking the pretest probability (your initial estimate) and adjusting it using the test’s performance (sensitivity and specificity) via Bayes’ theorem.

Think of it this way: the pretest probability is where you started before testing. If the test is positive, you move to a higher posttest probability of disease (P(Disease | positive)); if the test is negative, you move to a different posttest probability (P(Disease | negative)). Positive predictive value and negative predictive value are specific posttest probabilities conditioned on the test outcome, but the general term for the updated probability after testing is posttest probability.