Table 3.

Sensitivity analysis: the variables in the zero-part were chosen following a backward selection based on the Akaike information criterion (AIC) of the zero-inflated Poisson (ZIP) model instead of the hurdle model (compare Table 2).

		ZIP			Hurdle
		exp($\widehat{\mathrm{\beta }}$)	SE	p-Value	exp($\widehat{\mathrm{\beta }}$)	SE	p-Value
Count-part	Intercept	1.54	0.38	0.264	2.61	0.41	0.018
	Moving single pigs	1.82	0.23	0.008	1.73	0.24	0.023
	Separate pen for diseased pigs	1.66	0.20	0.011	1.44	0.21	0.084
	Use of purchased feed only	0.62	0.20	0.015	0.65	0.21	0.042
	Water birds in 1 km radius of farm	1.10	0.16	0.537	1.09	0.16	0.592
	Disinfection of livestock trail after housing out	1.39	0.27	0.229	0.99	0.26	0.977
	Disinfection of livestock trail less frequent than after housing out	1.13	0.32	0.703	0.83	0.31	0.555
	Disinfection with chlorine	1.30	0.19	0.158	1.20	0.19	0.318
	Number of fattening pigs (>1,000 to ≤1,500)	0.94	0.18	0.712	0.93	0.18	0.700
	Number of fattening pigs (>1,500)	1.59	0.19	0.018	1.42	0.20	0.082
Zero-parta	Intercept	0.38	0.68	0.151	0.40	0.58	0.114
	Use of purchased feed only	>1,000	>1,000	0.993	3.63	1.14	0.259
	Water birds in 1 km radius of farm	0.00	>1,000	1.000	0.19	1.26	0.185
	Number of fattening pigs (>1,000 to ≤1,500)	0.00	>1,000	1.000	0.22	1.20	0.214
	Number of fattening pigs (>1,500)	0.00	>1,000	0.988	0.15	1.30	0.148
	AIC	229.91			236.71

Estimates*, SEs, and p-values of the variables are given for the ZIP and hurdle model.

*Interpretation of estimates in the count model/count-part: a one unit change in the predictor variable is associated with a $\left(\text{1}-\text{exp}\left(\widehat{\mathrm{\beta }}\right)\right)\ast$ 100 percentage change of the expected sample count, holding other variables constant. Interpretation of estimates in the zero-part: a one unit change in the predictor variable is associated with a $\left(\text{1}-\text{exp}\left(\widehat{\mathrm{\beta }}\right)\right)\ast$ 100 percentage increase of the odds (chance) of not having any positive samples.

^aThe ZIP model estimates the probability for zero inflation and the hurdle model estimates the probability for hurdle crossing (non-zeros). Therefore, the estimates of the hurdle model were multiplied by (−1) to make them comparable to the ZIP model.

Bold: p-values that passed the significance threshold (p < 0.05).