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Table 2 Minimum sample sizes required to estimate freedom from Johne’s Disease (JD) at the herd level, using an imperfect test and adjusting for a finite population calculated using the AusVet EpiTool Epidemiological calculator (URL: http://epitools.ausvet.com.au)

From: Use of a voluntary testing program to study the spatial epidemiology of Johne’s disease affecting dairy herds in Minnesota: a cross sectional study

Herd size (number of cows)Sample sizea
5–20N/A (Recommendation: Same as herd size)
21–2520
26–4024
41–5525
56–6526
66–8027
81–9528
96–10029
101–25030
> 25131
  1. aAssumptions: a) design prevalence, i.e. expected within herd prevalence =10%, b) sensitivity of the diagnostic test of 52%, and c) expected number of test infected cows in a herd is a product of herd size and the design prevalence