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Estimating specificity in uninfected populations

One special case of a gold standard comparison is for estimating test specificity in an uninfected population. In this case either historical information or other testing can be used to determine that a defined population is free of the disease of concern. This can be based on either a geographic region which is known to be free, or on intensive testing of a herd or herds over a period of time to provide a high level of confidence of freedom. If the population is assumed to be free, by definition all animals in the population are uninfected. Therefore, if a sample of animals from the population is tested with the new test, any positives are assumed to be false positives and the test specificity is estimated as the proportion of samples that test negatively.