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Risk-based surveillance

These calculators can be used for the simple analysis of risk-based surveillance. They are simplified versions of the scenario-tree modelling tools for the analysis of complex surveillance systems to demonstration freedom from disease or for the early detection of disease (available at These calculators use simple common surveillance system structures that allow the calculation of the sensitivity of a risk-based or biased surveillance system, and the calculation of the required sample size to achieve a target sensitivity.

Click here for some important formulae for freedom analyses.

1-stage survey with single risk factor

2-stage survey with single risk factor at cluster level

Population sensitivity and confidence of freedom

2-stage survey with risk factors at both cluster and unit levels

This site was created by Ausvet with funding from a range of sources. It provides a range of epidemiological tools for the use of researchers and epidemiologists. Please submit any comments, questions or suggestions here.