HerdPlus utilities

HerdPlus: SeH and SpH comparison for varying herd sizes

Test sensitivity

Test specificity

Animal-level design prevalence value

Minimum herd size

Maximum herd size

Sample size

Cut-point number of reactors

Precision (significant digits)

Iterations

100 1000 10000

Submit

Calculate herd sensitivity and herd specificity for a range of herd sizes, for specified test sensitivity, test specificity, sample size and cut-point 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;
• Animal-level 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 cut-point number of reactors to classify a herd/flock as positive (if there are fewer reactors than the specified cut-point the herd is negative, if the number of reactors is >= cut-point 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. Herd-level test performance based on uncertain estimates of individual test performance, individual true prevalence and herd true prevalence. Prev. Vet. Med. 3: 187-209; and
• FreeCalc: Cameron AR, Baldock FC, 1998. A new probability formula for surveys to substantiate freedom from disease. Prev. Vet. Med. 34: 1-17.

Acknowledgement

Developed by Matthias Greiner and Evan Sergeant