Sensitivity:- It is defined as the ability of a test to identify correctly all those who have the disease (True positives) Specificity:- It is defined as the ability of a test to identify correctly those who do not have the disease (True Negatives) Diagnostic power of the test . Positive predictive value:- Indicates the probability of a person with a positive test result having the disease. It depends on sensitivity, specificity of the test and prevalence of the disease. It is directly propoional with the prevalence of the disease. Negative predictive value:- Probability a person with a negative test result not having the disease Ref:- K Park, 24th ed; pg num:- 149-150