Table 5.
Parameter coefficients and fit for the four exponential random graph models (ERGMs) of pig trade in a small-scale production system (Bulgaria).
| Covariates | ERGM coefficients (SE)a |
|||
|---|---|---|---|---|
| Bernoulli (edges) | Edges + attributes | Edges + network statistics | Edges + attributes + network statistics | |
| Edges | −7.30 (0.03)*** | −10.18 (0.30)*** | −9.62 (0.67)*** | |
| Link attributes | ||||
| Distance (km) | −0.07 (0.00)*** | −0.07 (0.00)*** | ||
| Nodal attribute mixing | ||||
| Regionb | ||||
| E to E | 0.02 (0.16) | −0.88 (0.53) | ||
| NW to E | 0.08 (0.48) | −0.36 (1.02) | ||
| S to E | 0.92 (1.02) | 1.85 (1.60) | ||
| SW to E | NA | NA | ||
| E to NW | 0.57 (0.38) | −0.51 (0.74) | ||
| NW to NW | −1.29 (0.13)*** | −0.82 (0.44) | ||
| S to NW | NA | NA | ||
| SW to NW | −1.43 (1.01) | 3.10 (1.66) | ||
| E to S | 3.50 (0.32)*** | 3.89 (0.68)*** | ||
| NW to S | 1.61 (0.37)*** | 1.75 (0.62)** | ||
| S to S | Reference | Reference | ||
| SW to S | NA | NA | ||
| E to SW | 15.91 (0.49)*** | 20.78 (0.99)*** | ||
| NW to SW | 2.55 (0.31)*** | 6.49 (0.68)*** | ||
| S to SW | 3.77 (0.45)*** | 5.68 (1.06)*** | ||
| SW to SW | 0.39 (0.36) | 1.75 (0.93) | ||
| Type of farmc | ||||
| SP to SP | Reference | Reference | ||
| IN to SP | 2.37 (0.17)*** | 0.75 (0.24)** | ||
| TA to SP | 2.20 (0.12)*** | 0.92 (0.17)*** | ||
| TB to SP | 1.98 (0.08)*** | 0.82 (0.10)*** | ||
| SP to IN | −1.45 (1.00) | −1.08 (1.33) | ||
| IN to IN | 3.33 (0.28)*** | 2.31 (0.93)* | ||
| TA to IN | 1.19 (0.52)* | 1.43 (1.16) | ||
| TB to IN | 0.58 (1.01) | 0.14 (1.74) | ||
| SP to TA | −0.81 (0.45) | 0.09 (0.68) | ||
| IN to TA | 2.95 (0.25)*** | 2.22 (0.78)** | ||
| TA to TA | 1.26 (0.37)*** | 1.24 (0.83) | ||
| TB to TA | 2.26 (0.32)*** | 2.16 (0.69)** | ||
| SP to TB | −1.03 (0.26)*** | 0.73 (0.44) | ||
| IN to TB | 3.08 (0.29)*** | 3.32 (0.71)*** | ||
| TA to TB | 2.72 (0.24)*** | 3.22 (0.55)*** | ||
| TB to TB | 1.92 (0.22)*** | 2.49 (0.59)*** | ||
| Structural terms | ||||
| Asymmetric edges | NS | 1.31 (0.40)** | ||
| GWID | 10.18 (0.30)*** | 10.44 (0.35)*** | ||
| GWDSP | −2.72 (0.07)*** | −2.52 (0.09)*** | ||
| GWESP | 4.59 (0.29)*** | 2.28 (0.36)*** | ||
| Fit | ||||
| Akaike information criteria | 20,372 | 14,940 | 17,394 | 12,397 |
a*** <0.001; ** <0.01; * <0.05.
bE, east; NW, north-west; S, south; SW, south-west.
cSP, small producer; IN, industrial; TA, type A; TB, type B.