Table 4 Parameter estimates for conventional and selectivity SPF models: Unmatched sample

lnENGINEOPER

0.79***

(0.07)

0.69***

(0.13)

0.84***

(0.09)

0.72***

(0.16)

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

0.17**

(0.08)

0.06

(0.12)

0.23**

(0.11)

0.06

(0.19)

0.23*

(0.12)

lnHELPERSEMP

 − 0.05

(0.13)

0.24

(0.19)

 − 0.20

(0.18)

0.23

(0.29)

 − 0.21

(0.20)

lnUSEFULSEINE

0.06**

(0.03)

0.09**

(0.04)

0.05

(0.03)

0.09

(0.07)

0.05

(0.04)

ONDO

0.09**

(0.04)

0.13

(0.10)

0.07

(0.05)

0.05

(0.13)

0.05

(0.06)

AKWA-IBOM

0.09**

(0.04)

0.17**

(0.08)

0.05

(0.05)

0.12

(0.10)

0.04

(0.06)

SHOCK

0.07**

(0.03)

0.06

(0.06)

0.08**

(0.04)

0.06

(0.08)

0.09*

(0.05)

HIGHENGCAP

 − 0.12

(0.10)

 − 0.31**

(0.15)

 − 0.02

(0.13)

 − 0.30

(0.23)

 − 0.01

(0.19)

FISHVILL

 − 0.01

(0.03)

 − 0.09*

(0.05)

0.01

(0.04)

 − 0.11

(0.09)

0.01

(0.05)

Leadercontrol

 − 0.04

(0.04)

0.00

(0.07)

 − 0.07

(0.06)

 − 0.002

(0.09)

 − 0.07

(0.06)

Helpercontrol

 − 0.03

(0.10)

0.17

(0.16)

 − 0.12

(0.13)

0.16

(0.26)

 − 0.13

(0.15)

MEMBERSHIP

0.11***

(0.04)

Constant

9.28

(0.48)

8.44***

(0.68)

9.73***

(0.63)

8.60***

(0.95)

9.66***

(0.72)

λ

1.18***

(0.06)

1.12***

(0.21)

1.28***

(0.07)

\({\sigma }^{2}\)

0.13***

(0.02)

0.09***

(0.05)

0.14***

(0.02)

\({\sigma }_{u}\)

0.23*

(0.13)

0.28***

(0.07)

\({\sigma }_{v}\)

0.21***

(0.05)

0.25***

(0.04)

\({\rho }_{(w,v)}\)

0.43

(0.47)

 − 0.32

(0.34)

Return to scale

1.12

0.93

1.07

0.86

1.06

Number of obs

353

95

258

95

258

Log likelihood

 − 51.69

2.96

 − 46.22

 − 80.40

 − 114.32