1-Stage Freedom analysis

Population level (or herd, flock, cluster, or other grouping) sensitivity

Design prevalence (proportion or units)

Unit (test or cluster) sensitivity

Sample size

Population size (if known)

Submit

This utility calculates a population or cluster level sensitivity for a survey. This is the probability (or level of confidence) that one or more positive units would be detected if the disease was present at a prevalence greater than or equal to the specified design prevalence.

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

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;
• Sample size - the number of units sampled (animals or clusters); 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:

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