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HerdPlus utilities

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

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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.


Developed by Matthias Greiner and Evan Sergeant