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Table 5 Proportion of serum samples testing antibody positive and agreement between two HI tests in ducks naturally exposed to H5 avian influenza virus

From: Comparison of serological assays for detecting antibodies in ducks exposed to H5 subtype avian influenza virus

  HI-CRBC HI-HRBC
Proportion positive (95%-CI)1 0.02 (0.0-0.04) 0.08 (0.03-0.13)
Dichotimized results:  
Kappa (95%-CI)2 0.40 (0.24-0.57)
PABAK 0.88
Log titers:   
Weigthed Kappa (95%-CI)3 0.53 (0.45-0.62)
PABAK 0.94
  1. 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.
  2. 1Confidence intervals for the proportion of positives were adjusted for clustering of ducks by farm (54 clusters).
  3. 2The analytical method was used to calculate confidence intervals for dichotomised test results [35].
  4. 3The bootstrap method with 100 bootstrap replications was used to calculate confidence intervals for the log titers [36, 37].
  5. 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).