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Agricultural and Food Economics
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Table 5 Parameter estimates of SPF model

From: Correcting for sample selection in stochastic frontier analysis: insights from rice farmers in Northern Ghana

Variable Convectional SPF Sample selection SPF
Pooled Irrigation only Rainfed only Pooled—sample Irrigation Rainfed
Coef. Std. Err. Coef. Std. Err. Coef. Std. Err. Coef. Std. Err. Coef. Std. Err. Coef. Std. Err.
Const. 3.988c 0.044 3.944c 0.062 4.053c 0.063 3.970c 0.066 3.942c 0.023 4.007c 0.114
Farm size 0.920c 0.074 1.205c 0.011 1.283c 0.095 0.923c 0.084 1.336c 0.034 1.144 0.122
Labour 0.067a 0.04 0.044 0.071 0.256c 0.093 0.069 0.053 0.023 0.018 0.11 0.102
Seed − 0.235c 0.027 − 0.157c 0.045 − 0.235c 0.051 − 0.158c 0.034 − 0.153c 0.016 − 0.107 0.08
Fertilizer − 0.014 0.047 0.053 0.108 − 0.127b 0.057 − 0.018 0.049 0.132c 0.028 − 0.071 0.113
Herbicide 0.124a 0.064 − 0.266 0.221 − 0.074 0.102 0.062 0.081 − 0.520c 0.047 − 0.076 0.138
Farm size2 0.076c 0.026 0.183c 0.042 − 0.071b 0.035 0.013 0.02 0.224c 0.01 − 0.085b 0.036
Labour2 − 0.0198 0.017 − 0.0187 0.017 0.025 0.03 − 0.014 0.02 − 0.0098a 0.005 0.0022 0.038
Seed2 − 0.046c 0.006 − 0.014 0.01 − 0.060c 0.011 − 0.044c 0.007 − 0.012c 0.002 − 0.036b 0.015
Fertilizer2 0.004 0.011 0.006 0.014 − 0.025 0.015 − 0.012 0.009 0.051c 0.007 − 0.0277 0.035
Herbicide2 − 0.033 0.03 0.104 0.073 − 0.022 0.034 − 0.054 0.037 0.145c 0.022 − 0.04223 0.061
Farm sizeaLabour 0.0756 0.058 − 0.009 0.066 0.207a 0.125 0.066 0.067 − 0.052b 0.021 0.26375a 0.142
Farm sizeaSeed − 0.036 0.048 − 0.069 0.056 − 0.085 0.064 0.0097 0.049 − 0.071c 0.017 − 0.06171 0.089
Farm sizeaFertilizer − 0.234c 0.072 0.175a 0.09 0.009 0.102 0.235c 0.072 0.173c 0.027 − 0.17683 0.139
Farm sizeaHerbicide − 0.013 0.088 − 0.379b 0.151 0.159 0.11 0.182c 0.066 0.473c 0.042 0.28069b 0.123
LabouraSeed 0.049a 0.027 0.026 0.034 − 0.145c 0.051 − 0.038 0.034 0.0063 0.008 − 0.09272 0.065
LabouraFertilizer 0.037 0.052 − 0.034 0.073 − 0.012 0.068 0.072 0.059 − 0.016 0.021 0.05588 0.105
LabouraHerbicide − 0.065 0.063 − 0.075 0.074 − 0.02 0.125 − 0.087 0.07 − 0.036 0.025 − 0.1116 0.133
SeedaFertilizer 0.091b 0.036 − 0.055 0.069 0.214c 0.06 0.132c 0.04 − 0.093c 0.017 0.20680b 0.103
SeedaHerbicides 0.131c 0.046 0.06 0.086 0.178c 0.058 0.056 0.054 0.071c 0.022 0.08807 0.082
FertilizeraHerbicide 0.042 0.073 − 0.288b 0.117 − 0.151 0.093 0.03 0.074 − 0.458c 0.035 − 0.01806 0.139
RTS 0.86   0.88   1.10   0.88   0.82   1.00  
L. Likelihood − 362.855 − 35.986 − 235.691 − 671.929 − 187.078 − 408.302
gamma(γ) 0.947 0.969 0.972       
lambda(λ)        2.056 9.093 1.324
σ(u) 4.212c 0.525 5.618c 1.593 5.866c 1.336 0.689c 0.047 0.644c 0.012 0.627c 0.098
σ (v) 0.807c 0.001 0.503c 0.002 0.907c 0.002 0.335c 0.031 0.071c 0.01 0.474c 0.06
Selectivity bias (ρw,v)        0.727c 0.085 0.99998c 0.001 0.823c 0.092
N 538 223 315 538 223 315
  1. a, b and c represent 10%, 5% and 1% level of significance, respectively
  2. Source: Analysis of field data, 2017
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