About This Figure
Understanding Test Results for Infectious Diseases
The illustration depicts the likelihood of false positive and false negative test results based on the prior probability of a disease occurring in a given population. Clinicians should consider the likelihood of disease before performing laboratory testing. The likelihood that a patient has a disease depends on many factors: Has a patient been in an area where the disease is found? Does the patient have signs and symptoms typical of the disease? Does the patient have risk factors for contracting or developing the disease? In populations where disease is rare or unlikely, testing is likely to lead to false positives more frequently than true positives.