Table 5 Parameter estimates for conventional and selectivity SPF models: Matched sample
| lnTOTALCAP | Conventional SPF | Sample selection SPF | |||
|---|---|---|---|---|---|
| Pooled | MEM | CONN | MEM | CONN | |
| Coeff | Coeff | Coeff | Coeff | Coeff | |
| lnENGINEOPER |
0.79*** (0.07) |
0.66*** (0.13) |
0.84*** (0.09) |
0.70*** (0.17) |
0.83*** (0.11) |
| lnFUELCOST |
0.10** (0.04) |
0.16*** (0.06) |
0.08 (0.05) |
0.14* (0.08) |
0.08 (0.06) |
| lnLEADERSEMP |
0.18** (0.08) |
0.08 (0.12) |
0.23** (0.11) |
0.09 (0.18) |
0.23* (0.12) |
| lnHELPERSEMP |
− 0.07 (0.14) |
0.22 (0.20) |
− 0.20 (0.18) |
0.20 (0.30) |
− 0.21 (0.20) |
| lnUSEFULSEINE |
0.06** (0.04) |
0.09** (0.04) |
0.05 (0.03) |
0.10 (0.05) |
0.05 (0.04) |
| ONDO |
0.09** (0.04) |
0.12 (0.10) |
0.07 (0.05) |
0.05 (0.13) |
0.05 (0.06) |
| AKWA-IBOM |
0.08* (0.04) |
0.16** (0.08) |
0.05 (0.05) |
0.11 (0.10) |
0.04 (0.06) |
| SHOCK |
0.07** (0.03) |
0.07 (0.06) |
0.08** (0.04) |
0.06 (0.08) |
0.09* (0.05) |
| HIGHENGCAP |
− 0.12 (0.10) |
− 0.30** (0.14) |
− 0.02 (0.13) |
− 0.30 (0.22) |
− 0.01 (0.19) |
| FISHVILL |
− 0.02 (0.03) |
− 0.10* (0.05) |
0.01 (0.04) |
− 0.12 (0.09) |
0.01 (0.05) |
| Leadercontrol |
− 0.04 (0.05) |
0.02 (0.07) |
− 0.07 (0.06) |
− 0.02 (0.09) |
− 0.07 (0.06) |
| Helpercontrol |
− 0.04 (0.10) |
0.16 (0.16) |
− 0.12 (0.13) |
0.14 (0.26) |
− 0.13 (0.15) |
| MEMBERSHIP |
0.12*** (0.04) | ||||
| Constant |
9.29*** (0.48) |
8.49*** (0.70) |
9.73*** (0.63) |
8.70*** (0.94) |
9.66*** (0.72) |
| λ |
1.19*** (0.06) |
1.20*** (0.19) |
1.28*** (0.07) | ||
| \({\sigma }^{2}\) |
0.13*** (0.02) |
0.09*** (0.04) |
0.14*** (0.02) | ||
| \({\sigma }_{u}\) |
0.24* (0.12) |
0.28*** (0.07) | |||
| \({\sigma }_{v}\) |
0.20*** (0.05) |
0.25*** (0.04) | |||
| \({\rho }_{(w,v)}\) |
0.45 (0.52) |
− 0.33 (0.34) | |||
| Return to scale | 1.13 | 0.91 | 1.07 | 0.84 | 1.06 |
| Number of obs | 350 | 92 | 258 | 92 | 258 |
| Log likelihood | − 52.17 | 0.67 | − 46.22 | − 80.01 | − 113.68 |