Table 1. Values used to calculate sample size in order to estimate farm-level prevalence.

Variable	Value	Ref
Herd size	5–20	Pilot study
No. lactating animals sampled	1–9	Inputted value
Design prevalence (min)	0.2	Inputted value
Individual test sensitivity (milk ELISA)	0.98	[16–19]
Individual test specificity (milk ELISA)	0.99
Calculated herd sensitivity (min)	0.72	http://epitools.ausvet.com.au/content.php?page=HerdSens4
Calculated herd specificity	0.95
Expected herd-prevalence	0.25	Expert opinion
Desired Precision (confidence)	0.06 (0.95)	Inputted value
No. farms in study area	10,000	Calculated from Census of India. 2011
Calculated sample size–unadjusted for clustering	384	Purposefully-designed spreadsheet
Design effect	1.07	Assumed from previous studies
Total herds–adjusted for clustering	411