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

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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%.


See sensitivity and specificity