Diagnostic specificity
= Diagnostic specificity
{title2=$Sp=P(-\mid\text{condition absent})$}
<Diagnostic specificity> is the probability that a test is negative in someone without the target condition. For an antibody test, relevant negative controls can include samples with antibodies to related pathogens to assess cross-reactivity. With true positive fraction $p$, observed positivity is $Se\,p+(1-Sp)(1-p)$.