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Table 3 Final multivariable model obtained using assumptions of the Gaussian distribution or exact method

From: Spread of porcine circovirus associated disease (PCVAD) in Ontario (Canada) swine herds: Part II. Matched case-control study

Variable Odds Ratio 95% Conf. Interval P a Overall Pb
Final model obtained based on the maximum likelihood method using assumption of Gaussian distribution
Ownership-adjusted high-risk local exposure
(OWHRLE; No high-risk local exposure = ref)
    <0.001
   High-risk local exposure within ownership 8.4E+6 (not estimated) 0.982  
   High-risk local exposure outside of ownership 1.32 (0.54, 3.22) 0.542  
Easting (100 kms) 1.65 (1.22, 2.21) 0.001 <0.001
Herd PRRSv status (positive) 2.25 (1.18, 4.28) 0.013 0.008
N obs = 680; n groups = 170, LR chisq = 29.4, df = 4, P < 0.001, AIC = 450
Adjusted estimates of the high-risk local exposure obtained using exact logistic regression c
Ownership-adjusted high-risk local exposure
(OWHRLE; No high-risk local exposure = ref)
    <0.001
   High-risk local exposure within ownership d 25.65 (3.40, +Inf) <0.001  
   High-risk local exposure outside of ownership 1.27 (0.45, 3.30) 0.640  
Easting binary (>600 km east = 1) 1.81 (0.53, 5.62) 0.378 0.378
Herd PRRSv status (positive) 1.93 (1.02, 3.91) 0.04 0.04
N obs = 680; n groups = 170, Model score = 19.98, P < 0.001
  1. a P-values are based on the Wald test for estimates of a model obtained using maximum likelihood method and based on Score test for estimates obtained using exact method.
  2. b Overall P-values are based on the likelihood ratio test for estimates of a model obtained using maximum likelihood method and based on Score test for estimates obtained using exact method.
  3. c Estimates of the local spread where obtained from the exact logistic regression after adjusting for the herd PRRS status and easting as a binary variable. Adjustment for the easting as a continuous explanatory variable could not be evaluated.
  4. d Best median unbiased estimates.
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