TABLE 4:

Illustrative power estimates were obtained from 10 000 simulations per scenario. Follow-up varied from two to four years with 1–3 comparison areas per culling area

Number of culling areasNumber of comparison areas per culling area
1 per culling area (Equation) (%)1 per culling area (Simulation) (%)2 per culling area (Simulation) (%)3 per culling area (Simulation) (%)
(a) Based on 2 years of follow-up
 29.49.811.712.5
 312.112.715.316.6
 414.815.118.320.2
 517.417.621.924.1
 620.019.725.427.6
(b) Based on 3 years of follow-up
 246.145.456.561.6
 362.661.973.979.2
 475.074.785.889.7
 583.883.992.895.2
 689.789.796.297.4
(c) Based on 4 years of follow-up
 272.673.284.688.6
 388.088.895.397.2
 495.295.598.799.4
 598.298.399.899.9
 699.399.4100.0100.0
  • The power based on the equation given above (with one comparison area) was also given for comparison. Each area was assumed to contain 200 annually tested herds and to have a baseline incidence of OTFW herd incidents of 0.15 per herd per annum. The impacts of culling were assumed to be the estimates presented in Table 1

  • OTFW, official tuberculosis-free status of the herd withdrawn