A total of 518 ducks were sampled in December 2008. The kappa statistic (95% confidence interval1) was used to compare dichotomised test results (positive versus negative) and a weighted kappa statistic (95% confidence interval2) was used to compare log titers.
1Confidence intervals for the proportion of positives were adjusted for clustering of ducks by farm (54 clusters).
2The analytical method was used to calculate confidence intervals for dichotomised test results .
3The bootstrap method with 100 bootstrap replications was used to calculate confidence intervals for the log titers [36, 37].
Abbreviations: HI-CRBC (Haemagglutination inhibition test using chicken red blood cells), HI-HRBC (Haemagglutination inhibition test using horse red blood cells), CI (confidence interval), PABAK (Prevalence and bias adjusted kappa).