Herd-level sensitivity and specificity for testing in an infinite population

Design prevalence

Test sensitivity

Test specificity

Sample size

Submit

This utility estimates the probability of detecting disease (herd-sensitivity) in a large (infinite) population, if it is present at the specified design prevalence, assuming a test of known sensitivity and specificity and that all samples have a negative test result. These analyses use the method from Martin et el. (1992) (Prev Vet Med, 14:33-43), assuming known test sensitivity and test specificity and a cut-point number of reactors of 1 to declare a population infected (i.e. to be recognised as free there must be zero positive reactors). See also Richards, MS (1983). Proceedings of the 3rd International Symposium on Veterinary Epidemiology and Economics, pp 567-570.

Inputs are:

• Sample size tested;
• Test sensitivity;
• Test specificity; and
• Design (target) prevalence.

Outputs are:

• The herd-level sensitivity and specificity for the given sample size, test sensitivity, test specificity and design prevalence; and
• A table and graph of herd-sensitivity values for a range of design prevalence and sample size values and herd-specificity for the same range of sample sizes.