Features of diagnostic test that can be calculated by comparison with gold standard in validation study

Feature of the testAlternative nameQuestion addressedFormula (see table 2)
SensitivityTrue positive rate (positive in disease)How good is this test at picking up people who have the condition?a/ (a+c)
SpecificityTrue negative rate (negative in health)How good is this test at correctly excluding people without the condition?d/ (b+d)
Positive predictive valuePost-test probability of a positive testIf a person tests positive, what is the probability that he or she has the condition?a/ (a+b)
Negative predictive valuePost-test probability of a negative testIf a person tests negative, what is the probability that he or she does not have the condition?d/ (c+d)
AccuracyWhat proportion of all tests have given the correct result? (true positives and true negatives as a proportion of all results)(a+d)/ (a+b+c+d)
Likelihood ratio of a positive testHow much more likely is a positive test to be found in a person with the condition than in a person without it?sensitivity/ (l-specificity)
Likelihood ratio of a negative testHow much more likely is a negative test to be found in a person without the condition than in a person with it(l-sensitivity)/specificity?