TABLE 3:

Illustrative sample sizes in terms of the number of matched pairs of culling and comparison areas required for at least 80 and at least 90 per cent power

200 annually tested herds per area and baseline incidence of OTFW herd incidents of 0.15 per herd per annum (or 0.10 per herd per annum)100 annually tested herds per area and baseline incidence of OTFW herd incidents of 0.15 per herd per annum (or 0.10 per herd per annum)
Time under observationAt least 80% powerAt least 90% powerAt least 80% powerAt least 90% power
 1 year397 (595)531 (797)793 (1190)1062 (1593)
 2 years37 (56)50 (74)74 (111)99 (148)
 3 years5 (7)7 (10)10 (14)13 (19)
 4 years3 (4)4 (5)5 (8)7 (10)
  • OTFW, official tuberculosis-free status of the herd withdrawn