1-Stage Freedom analysis

Sample size to achieve specified population level (or herd, flock, cluster, etc) sensitivity

Design prevalence (proportion or units)

Unit (test or cluster) sensitivity

Required population sensitivity

Population size (if known)

Submit

This utility calculates the sample size required to achieve a target population or cluster level sensitivity for a survey.

For these calculations unit specificity is assumed to be 100%. For cluster (herd, flock, etc) level calculations, enter test sensitivity, unit-level design prevalence and required cluster-level sensitivity. Alternatively, for population level calculations enter cluster-level (herd) sensitivity, cluster-level design prevalence and required population-level sensitivity.

Calculations use the hypergeometric approximation if population size is provided, or binomial method if population size is not specified.

Inputs are:

• Design prevalence as either a proportion or an integer number of units (animals for cluster level sensitivity and clusters for population-level sensitivity);
• Unit sensitivity (test sensitivity to calculate cluster (herd) sensitivity or cluster (herd) sensitivity to calculate population sensitivity;
• Required population-level sensitivity; and
• Population size (optional if design prevalence is specified as a proportion, required if design prevalence is a number of units). Leave population size blank if not known.

Outputs are:

• Required sample size for the given target population sensitivity, design prevalence and unit sensitivity; and
• A table and graph of sample sizes for varying population and design prevalence values and the given target population sensitivity and unit sensitivity.