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

From: Can producer groups improve technical efficiency among artisanal shrimpers in Nigeria? A study accounting for observed and unobserved selectivity

lnTOTALCAP Conventional SPF Sample selection SPF
Pooled MEM CONN MEM CONN
Coeff Coeff Coeff Coeff Coeff
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
  1. ***p < 0.01, **p < 0.05, *p < 0.1
  2. The results for pooled, MEM, and CONN models were estimated using Eq. (15). Standard errors are presented in parentheses
  3. Source: Authors’ calculation based on survey data