Sample size for demonstration of freedom (detection of disease) in a finite population

Population size (for finite populations)

Test sensitivity

Desired herd sensitivity

0.9 0.95 0.98 0.99

Design prevalence

Submit

This utility calculates the sample size required to provide a desired probability of detecting disease (herd-sensitivity) at the specified design prevalence, for a finite population, assuming a test of known sensitivity and 100% specificity. These analyses use an approximation of the hypergeometric distribution (MacDiarmid, SC (1988). NZ Vet J, 36:39-42).

Inputs are:

• Size of the population;
• Test sensitivity;
• Desired herd-sensitivity; and
• Design (target) prevalence.

Outputs are:

• The number of samples required to be tested to provide the desired herd-sensitivity for the given design prevalence; and
• A table and graph of sample sizes required to provide the desired herd-sensitivity, for the specified test sensitivity and a range of population sizes and design prevalences.