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Table 6 Results of zero-inflation Poisson regression modelling for the offset-model (Model 1: offset if log-size of number of tested animals), for the model treating log-size as a free covariate (Model 2) and the model with a quadratic term included (Model 3) based upon the CSFS data with index cases removed from the data set (n = 174).

From: On the question of proportionality of the count of observed Scrapie cases and the size of holding

Model 1

coefficient

S.E.

Z = coeff./S.E.

log-likelihood (AIC, BIC)

α

-4.3154

0.1091

-39.56

-208.00

β 1

1 (fixed)

  

(420.00, 426.32)

Model 2

coefficient

S.E.

Z = coeff./S.E.

log-likelihood (AIC, BIC)

α

-3.9731

1.1692

-3.40

-207.96

β 1

0.9332

0.2275

4.10

(421.92, 431.40)

Model 3

coefficient

S.E.

Z = coeff./S.E.

log-likelihood (AIC, BIC)

α

-6.3097

5.1816

-1.22

-207.83

β 1

1.9721

2.2259

0.89

(423.67, 436.30)

β 2

-0.1130

0.2387

-0.47