Table 2.

Summary of linear regression model

		Multivariate model
Variable	Description	β Coefficient	Standard error	P-value
Intercept		-0.045	0.008	< .001
Production	Conventional	-0.003	0.004	0.400
	Organic	0	-	-
Herd size	< 100	0.010	0.007	0.175
	100 to 200	0.003	0.008	0.734
	> 200	0	-	-
State	NY	0.003	0.004	0.463
	OR	0.013	0.007	0.069
	WI	0	-	-
Johne’s procedures	Cull after calving or dry off	0.020	0.009	0.025
	Cull immediately	0.010	0.005	0.035
	Keep	0.018	0.007	0.019
	Never observed clinical Johne’s disease	0	-	-
Seasonality	$$\mathit{Cosine}\left(2\pi \frac{\mathit{Day}}{365}\right)$$	-0.030	0.003	< .001

Linear regression model on Mycobacterium avium subsp. paratuberculosis ELISA optical density from bulk tank milk samples of 233 farms. Multivariate model was built by backwards stepwise elimination and started with all variables listed in Table 1.