Table 4.

Model 2.

Variable	n	Coefficient	SE	p	CIa		OR	CIb
Intercept		2.48	0.25
Age category
8 weeks		reference					reference
14 weeks	16	-0.06	0.2	0.76	-0.45	0.33	reference
Gilts	16	0.52	0.2	0.01	0.12	0.92	reference
Parity 1	16	0.93	0.2	< 0.01	0.53	1.33	10.8	3.54	33.02
Parity 2	16	1.14	0.21	< 0.01	0.74	1.54	16.3	5.44	48.84
Parity 3	16	1.19	0.2	< 0.01	0.79	1.59	18.8	6.4	54.88
Parity 4	16	1.08	0.2	< 0.01	0.68	1.48	12.72	4.21	38.41
Parity 5+	16	1.31	0.2	< 0.01	0.91	1.71	8.39	2.87	24.56
Distance to nearest pig unit (miles)	16	-0.06	0.02	< 0.01	-0.1	-0.01	0.88	0.78	0.99
Quarantine facilities on farm
Not present	4	reference
Present	12	-0.56	0.24	< 0.05	-1.02	-0.1	0.27	0.08	0.87
Estimation of random effects:
Variation between herds		0.12	0.06
Variation between pens		0.29	0.05
Variation between pigs		0.24	0.01

Multivariable three level mixed model of factors associated with log IRPC of 774 pigs belonging to 16 herds that had seronegative young stock.

Sample size (n); standard error (SE); probability function (p); 95% confidence interval (CI^a) when pigs' log IRPC (+12) values were used as a continuous outcome variable; Odds Ratios (OR) and 95% confidence interval (CI^b) when pig-level seropositivity (absence/presence of antibodies) was used as a comparative binary outcome variable (exp(coefficient+/-(1.96 × standard error))).