Table 6.

Parameter coefficients and fit for the four exponential random graph models (ERGMs) of pig trade in an extensive production system (Spain—Extremadura).

Covariates	ERGM coefficients (SE)a
	Bernoulli (edges)	Edges + attributes	Edges + network statistics	Edges + attributes + network statistics
Edges	−10.77 (0.02)***	−9.34 (0.04)***	−5.87 (0.26)***	−4.87 (0.55)***
Nodal attribute mixing
Housing systemb
In to in		−1.23 (0.05)***		−0.74 (0.06)***
In to out		−0.68 (0.04)***		−0.30 (0.05)***
Out to in		−0.68 (0.04)***		−0.56 (0.05)***
Out to out		Reference		Reference
Type of farmc
MU to MU		2.44 (1.00)*		2.09 (2.47)
MU to FA		1.79 (0.58)**		1.84 (0.88)*
MU to FF		−0.26 (0.27)		−0.34 (0.28)
MU to FI		−0.23 (0.38)		−0.41 (0.46)
MU to SP		NA		NA
FA to MU		1.38 (0.71)		0.83 (1.17)
FA to FA		0.07 (0.58)		−0.09 (0.82)
FA to FF		−0.39 (0.13)**		−0.45 (0.16)**
FA to FI		0.18 (0.13)		0.06 (0.18)
FA to SP		−0.89 (0.71)		−0.67 (0.87)
FF to MU		0.20 (0.22)		0.36 (0.32)
FF to FA		−0.67 (0.14)***		−0.28 (0.18)
FF to FF		−1.25 (0.05)***		−0.75 (0.06)***
FF to FI		−0.72 (0.05)***		−0.33 (0.06)***
FF to SP		−2.46 (0.26)***		−1.83 (0.28)***
FI to MU		0.47 (0.27)		0.28 (0.36)
FI to FA		−0.02 (0.15)		−0.05 (0.21)
FI to FF		−0.59 (0.05)***		−0.50 (0.06)***
FI to FI		Reference		Reference
FI to SP		−1.79 (0.27)***		−1.52 (0.31)***
SP to MU		0.15 (1.00)		0.96 (1.27)
SP to FA		NA		NA
SP to FF		−2.46 (0.26)***		−1.37 (0.29)***
SP to FI		−1.95 (0.29)***		−1.00 (0.30)***
SP to SP		−2.12 (1.00)*		−0.86 (1.39)
Structural terms
Isolates			1.08 (0.04)***	0.90 (0.06)***
Asymmetric edges			−1.99 (0.27)***	−2.28 (0.54)***
GWOD			−2.59 (0.06)***	−2.55 (0.08)***
GWDSP			−0.24 (0.02)***	−0.26 (0.03)***
GWESP			3.63 (0.27)***	4.34 (0.24)***
Fit
Akaike information criteria	96,949	94,851	91,182	89,952

^a*** <0.001; ** <0.01; * <0.05.

^bIn, indoor; Out, outdoor.

^cU, multipliers; FA, farrow farms; FF, farrow-to-finish farms; FI, finishers; SP, small producers.