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

To know the probability of SLE at this point,We need to know Prior probability (Prevalence) of each test, sensitivity and specificity of each test Probability of having a Disease means PPV i.e. Positive Predictive Value and it depends upon (BAYES'THEORM) sensitivity specificity and disease Prevalence