Posttest probability describes the probability of having the condition after testing.

Posttest probability describes the probability of having the condition after testing.

• A. Probability before testing
• B. Probability after testing
• C. Probability of disease in population
• D. Probability of test failure

Answer: (B)

Posttest probability is the probability of having the condition after you know the test result. It updates your initial assessment (the pretest probability) using the information from the test. In practice, a positive result raises the likelihood that the person truly has the disease, and a negative result lowers it. This description fits posttest probability because it’s about the probability after testing, not before testing, not the disease prevalence in a population, and not the chance the test fails.

Posttest probability is the probability of having the condition after you know the test result. It updates your initial assessment (the pretest probability) using the information from the test. In practice, a positive result raises the likelihood that the person truly has the disease, and a negative result lowers it. This description fits posttest probability because it’s about the probability after testing, not before testing, not the disease prevalence in a population, and not the chance the test fails.