Predictive value of tests

Predictive value of tests is the probability of a target condition (for example a disease) given by the result of a test, often in regard to medical tests.

In cases where binary classification can be applied to the test results (such yes or no, coulored or uncouloured, or either a positive or negative test) then each of the two outcomes has its separate predictive value. For example, for positive or negative test, the predictive values are termed positive predictive value or negative predictive value, respectively.

In cases where the test result is of a continuous value, the predictive value generally changes continuously along with the value. For example, for a pregnancy test that displays the urine concentration of hCG, the predictive value increases with increasing hCG value.

A conversion of continuous values into binary values can be performed, such as designating a pregnancy test as "positive" above a certain cutoff value, but this confers a loss of information and generally results in less accurate predictive values.

For more information on conversion and its disadvantages, see Artificial binary classification.