What formula expresses Positive Predictive Value (PPV)?

Positive Predictive Value (PPV) is a critical measure in diagnostic testing that evaluates the proportion of true positive results among all positive test results. It indicates how likely it is that a patient who has tested positive for a condition actually has that condition.

The formula for calculating PPV is derived from the concepts of true positives (TP) and false positives (FP). Specifically, PPV is expressed as the ratio of true positives to the sum of true positives and false positives. Thus, it can be formulated as TP divided by the total of TP and FP, which mathematically is represented as TP / (TP + FP).

This means that a high PPV indicates that a positive test result is likely to be accurate, whereas a lower PPV suggests that a significant proportion of positive results could be false positives. Understanding PPV is essential for interpreting diagnostic tests effectively, particularly in clinical settings where decisions about patient care may hinge on test outcomes.

The other options represent different statistical measures, such as negative predictive value or other combinations of true and false positive rates, which do not define the PPV.