throat, then the ppv would be very useful. however the bacteria may colonise individuals in a harmless way and never result in infection or disease. sore throats occurring in these individuals are caused by other agents such as a virus. in this situation the gold standard used in the evaluation study represents only the presence of bacteria (that might be harmless) but not a causal bacterial sore throat illness. it can be proven that this problem will affect positive predictive value far more than negative predictive value. to evaluate diagnostic tests where the gold standard looks only at potential causes of disease, one may use an extension of the predictive value termed the etiologic predictive value.