**Samples**

How many samples should I take?

This spreadsheet provides a guide to the number of samples that should be taken to find one or more positive samples.

The difficult issue is determination of the likely number of infected animals in a population

This presumes that the test has a 100% sensitivity

The formula is n=(1-(1-p^{(1/D)}
))*(N-0.5(D-1)

Where n = required number of samples

D= number of infected animals

N= total number of animals (groups, house, farm

p= degree of certainty required - for example 0.95 for 95%.