Almost daily, GPs are confronted with decisions about initiating tests or interpreting test results. Making decisions in this setting requires understanding the characteristics of the tests as well as the population in which the tests are being used.
Tests may be very good at detecting disease or, alternatively, they may be good at excluding disease. The value of a test depends also on how common the disease is in a population. The best screening test in the world for prostate cancer is not of much use in most women!