2-Stage surveys for demonstration of freedom

These utilities can be used to estimate sample sizes and to analyse results of 2-stage surveys for demonstrating disease freedom. For the first stage a sample of herds is selected while the second stage is to select a sample of animals from each selected herd. Current versions assume perfect test specificity but allow for imperfect sensitivity. Methods are also available for situations where a complete list of herd sizes is available and also where no information is available on the target population.

Click here for some important formulae for freedom analyses.

Sample size calculation

Use these options to calculate required sample sizes (clusters and units per cluster) assuming perfect test specificity:

• Least-cost sample sizes where herd sizes are known (and select clusters for testing)
• Least-cost sample sizes where herd sizes are NOT known
• Sample sizes for specified herd (cluster) sensitivity

Population sensitivity calculation (SSe)

Use these options to calculate population-level sensitivity assuming perfect test specificity:

• Analyse simple 2-stage freedom survey (fixed sample size)
• Analyse results of 2-stage freedom survey
• Stochastic analysis of 2-stage freedom survey