ABSTRACT
Suppose we wish to use a diagnostic test to help us decide whether a patient has a particular condition. We will assume that the result of the test is either positive or negative, where ‘positive’ is a diagnosis that the patient does have the condition, while ‘negative’ is a diagnosis that the patient does not have the condition. Suppose further that, in reality, the condition is either present or absent in the patient. We can now conceive of four types of situation, corresponding to the four categories in the following table:
