This utility estimates the probability of detecting disease (herd or cluster-sensitivity) in a large (infinite) population, if it is present at the specified design prevalence, assuming a test of known sensitivity and specificity and for a variable cut-point number of positives to determine the test result. These analyses use the method from Martin et el. (1992) (Prev Vet Med, 14:33-43) and the binomial distribution function, assuming known test sensitivity and test specificity and a variable cut-point number of positives to declare a population infected (i.e. a variable (non-zero) number of positive positives can be allowed and still be recognised as free). The population is classified as infected if the number of positive results is equal to or greater than the cut-point.