Definition
The Positive Predictive Value is defined as
where a "true positive" is the event that the test makes a positive prediction, and the subject has a positive result under the gold standard, and a "false positive" is the event that the test makes a positive prediction, and the subject has a negative result under the gold standard.
The following diagram illustrates how the positive predictive value, negative predictive value, sensitivity, and specificity are related.
Condition (as determined by "Gold standard") |
||||
Condition Positive | Condition Negative | |||
Test Outcome |
Test Outcome Positive |
True Positive | False Positive (Type I error) |
Positive predictive value = Σ True Positive Σ Test Outcome Positive |
Test Outcome Negative |
False Negative (Type II error) |
True Negative | Negative predictive value = Σ True Negative Σ Test Outcome Negative |
|
Sensitivity = Σ True Positive Σ Condition Positive |
Specificity = Σ True Negative Σ Condition Negative |
Note that the positive and negative predictive values can only be estimated using data from a cross-sectional study or other population-based study in which valid prevalence estimates may be obtained. In contrast, the sensitivity and specificity can be estimated from case-control studies.
If the prevalence, sensitivity, and specificity are known, the positive predictive value can be obtained from the following identity:
Read more about this topic: Positive Predictive Value
Famous quotes containing the word definition:
“The definition of good prose is proper words in their proper places; of good verse, the most proper words in their proper places. The propriety is in either case relative. The words in prose ought to express the intended meaning, and no more; if they attract attention to themselves, it is, in general, a fault.”
—Samuel Taylor Coleridge (17721834)
“The man who knows governments most completely is he who troubles himself least about a definition which shall give their essence. Enjoying an intimate acquaintance with all their particularities in turn, he would naturally regard an abstract conception in which these were unified as a thing more misleading than enlightening.”
—William James (18421910)
“It is very hard to give a just definition of love. The most we can say of it is this: that in the soul, it is a desire to rule; in the spirit, it is a sympathy; and in the body, it is but a hidden and subtle desire to possessafter many mysterieswhat one loves.”
—François, Duc De La Rochefoucauld (16131680)