HerdPlus utilities

HerdPlus: SeH and SpH for optimised sample sizes for range of herd sizes

Test sensitivity

Test specificity

Maximum herd sensitivity

Minimum herd specificity

Herd size range:

From

To

Maximum sample size relative to N

Animal-level design prevalence:

Calculate as 1/N for each herd size

Use specified proportion

Design prevalence value

Precision (significant digits)

Submit

Calculate optimised sample size and cut-point and resulting herd sensitivity (SeH) and herd specificity (SpH) for a specified range of herd sizes, test sensitivity, test specificity and design prevalence. Design prevalence can be specified as a fixed value, or as the equivalent of one animal per herd. Sample size and cut-point are constrained to provide SeH less than or equal to a specified maximum value and SpH greater than a specified minimum value. Sample sizes are also constrained to be no more than the specified proportion of herd size.

Inputs include:

• Test sensitivity and specificity;
• Maximum desired SeH and minimum SpH;
• Maximum sample size relative to herd size;
• Specified range of herd/population sizes;
• Mode of setting design prevalence, either as a specified value or as a proportion of herd size;
• Animal-level design prevalence (only required if option for specified design prevalence selected); and
• The desired precision of results (number of digits to be displayed after the decimal point).

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

• Table of optimised sample sizes and cut-points and corresponding SeH and SpH values for combinations herd sizes in specified range; and
• Plot of SeH and SpH values for optimised sample size and cut-point against herd size.

Acknowledgement

Developed by Matthias Greiner and Evan Sergeant