Table 1.
Sample size and confidence level (probability to detect animals with clinical signs) achieved in an establishment as a function of the herd size and the target (design) prevalence of animals with clinical signs (1%) and (0.5%), respectively. Sensitivity of the clinical examination Se = 75%
| Herd size | Example for (design) prevalence of animals with clinical signs 1% | Example for (design) prevalence of animals with clinical signs 0.5% | ||||
|---|---|---|---|---|---|---|
| (Design) Prevalence of animals with clinical signs | Sample size | Confidence level | (Design) Prevalence of animals with clinical signs | Sample Size | Confidence level | |
| 10 | 10%* | 10 | 74% | 10%* | 10 | 74% |
| 20 | 5%* | 20 | 74% | 5%* | 20 | 74% |
| 50 | 2%* | 50 | 75% | 2%* | 50 | 75% |
| 100 | 1% | 100 | 75% | 1%* | 100 | 75% |
| 200 | 1% | 200 | 94% | 0.5% | 200 | 75% |
| 250 | 1% | 250 | 94% | 0.5% | 250 | 75% |
| 300 | 1% | 253 | 95% | 0.5% | 300 | 94% |
| 500 | 1% | 300 | 95% | 0.5% | 500 | 94% |
| 750 | 1% | 312 | 95% | 0.5% | 527 | 95% |
| 1000 | 1% | 345 | 95% | 0.5% | 601 | 95% |
*
The minimum number of animals with clinical signs in a herd is one. Therefore, the values provided here for the design prevalence is the result of the ratio between 1 and the herd size.