Stochastic analysis of herd-testing data for 2-stage surveys for demonstrating disease freedom.
This analysis calculates the overall system sensitivity for the survey and the
resulting probability of population freedom from disease, allowing for uncertainty
about test sensitivity and/or prior probability of freedom. It assumes that a random sample of herds (or all herds) has been selected for testing
from the population and that a random sample of animals (or all animals) has been
tested within each selected herd. It also assumes that the test system has a specificity
of 100% (any positive results are further investigated to exclude false positives)
and that no positive results were recorded. The analysis adjusts for imperfect sensitivity
of the test used.
The analysis calculates both herd and system level sensitivity estimates using three
different methods depending on the available data:
Design prevalence (specified level of disease to be detected) must be specified
at both animal and herd levels. Design prevalence can be specified as either:
Inputs required include:
Outputs from the analysis include:
This analysis may take several minutes for large population sizes.
If you enter your email address below an email will
be sent to you with a link to the results.
Paste herd testing data in the space below. Data columns can be
in any order but must include a column for number tested (labeled "Tested"). Columns for herd id,
and herd size (labeled "HerdSize") are optional. A header row specifying column
names must also be included.
Download example data
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