You have diagnosed a patient clinically as having SLE and ordered 6 tests. Out of which 4 tests have come positive and 2 are negative. To determine the probability of SLE at negative. To determine the probability of SLE at this point, you need to know-

.sensitivity is the ability of a test to identify correctly those who actually have the disease,that is true positives.specificity is the ability of a test to identify correctly those who in actual do not have the disease.prior probability of disease such as SLE can be calculated by knowing these. ref:park&;s textbook,22 nd ed,pg 131