HerdPlus: SeH and SpH comparison for varying herd sizes

Input Values

Test Sensitivity:
Test Specificity:
Animal level design prevalence:
Minimum Herd Size:
Maximum Herd Size:
Sample Size:
Cut-point number of reactors:
Precision (significant digits):
Iterations:

Note:

This analysis may take several minutes if there is a wide range of herd sizes or a large number of iterations being run. Enter your email address and an email will be sent to you with a link to the results.

  

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:

  1. Simulated sampling using the specified number of iterations;
  2. HerdPlus: Using the hypergeometric distribution. Greiner et al, manuscript in preparation;
  3. 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
  4. 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


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