A term most used in the scientific literature to describe the selectivity of a test. It is the proportion of true negatives a test can produce. Mathematically, specificity is the number of true negatives divided by the sum of true negatives and false positives. The specificity of a test will determine its efficiency. If a PDD test can detect deception 100% of the time, but has a high false positive rate, it does not have good specificity and would have lower validity. Specificity and sensitivity are dimensions that characterize the validity of a test.