

Calculate herd sensitivity and herd specificity
for a range of herd sizes, for specified test sensitivity,
test specificity, sample size and
cutpoint number of reactors. For herd sizes that are less than the specified
sample size it is assumed that the whole herd is sampled.
Inputs include:
 Test sensitivity and specificity;
 Animallevel design prevalence (the hypothetical prevalence to be detected);
 Minimum and maximum size of the herds or flocks being sampled;
 Number of individuals tested (sample size);
 The cutpoint number of reactors to classify a herd/flock as positive
(if there are fewer reactors than the specified cutpoint the herd is negative,
if the number of reactors is >= cutpoint the herd is positive);
 The desired precision of results (number of digits to be displayed after the decimal point); and
 The number of iterations for the simulation method.
Tables and plots are presented for SeH and SpH for four different estimation methods:
 Simulated sampling using the specified number of iterations;
 HerdPlus: Using the hypergeometric distribution. Greiner et al, manuscript in preparation;
 HerdAcc: Jordan D, McEwen SA, 1998. Herdlevel test performance
based on uncertain estimates of individual test performance, individual true
prevalence and herd true prevalence. Prev. Vet. Med. 3: 187209; and
 FreeCalc: Cameron AR, Baldock FC, 1998. A new probability formula
for surveys to substantiate freedom from disease. Prev. Vet. Med. 34: 117
Acknowledgement:Developed by Matthias Greiner and Evan Sergeant
