Confidence of population freedom (NPV) for a surveillance system

Input Values

  

This calculator can be used to calculate the confidence of freedom (equivalent to negative predictive value) of a surveillance system. Assumptions are that:

  • Specificity of the testing regimen is assumed to be 100% - any positives detected on screening are followed up to confirm or refute the result; and
  • all test results (after follow-up) are negative.

Inputs are:

  • population-level sensitivity of the surveillance system (SSe for a population, SeH for an individual herd or flock); and
  • prior confidence of population freedom.

Output of the calculation is the posterior confidence that the population is free, given the negative surveillance data.

Population-level Sensitivity:
Prior confidence of freedom

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