Calculated using the conditional probability formula. Let event A: a person has the disease, event B: a person tests positive. By the known, P(A)=0.01,P(B|A~)=0.002,P(B~|A)=0.001. The probability of P(A~|B)=P(A~B)/P(B)=P(B|A~)*P(A~)/(P(B|A~)*P(A~)+P(B|A)*P(A))=0.002*0.99/(0.002*0.99+0.999+0.999). 0.99+0.999*0.01)=0.165=16.5%
Where ~ denotes taking the inverse, i.e., opposing events
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