# 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 http://freedom.ausvet.com.au). 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

### Population sensitivity and confidence of freedom

## 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

### Population sensitivity and confidence of freedom