HerdPlus utilities

HerdPlus: SeH and SpH for listed herd sizes and optimised sample sizes

Test sensitivity

Test specificity

Animal level design prevalence

Minimum herd sensitivity

Cut-point number of reactors

Precision (significant digits)

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Calculate herd sensitivity (SeH) and herd specificity (SpH) for specified herd sizes, optimised sample sizes (up to specified maximum), test sensitivity, test specificity, design prevalence and cut-point numbers of reactors. SeH and SpH are calculated for optimised sample sizes (constrained to <= specified maximum sample size for each herd size) to achieve given minimum SeH (or for given maximum sample size if minimum SeH is not achievable).

Inputs include:

• Test sensitivity and specificity;
• Animal-level design prevalence (the hypothetical prevalence to be detected);
• Minimum desired SeH;
• 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
• Pasted data containing columns of herd sizes and corresponding maximum sample sizes.

Results are calculated using the HerdPlus method (Greiner 2006?) and include:

• A table of optimised sample size and corresponding values for SeH and SpH for each specified herd size and maximum sample size; and
• A plot of SeH and SpH against herd size.

Acknowledgement

Developed by Matthias Greiner and Evan Sergeant