Rice Genomics and Genetics 2015, Vol.7, No.1, 1-10
9
X
11
=Access to improved rice seeds
X
12
=Agricultural training
X
13
=Off- farm employment
X
14
=Agricultural income
Equation (2) is estimated by maximum likelihood as
an independent probit model from the entire sample
of adopters and non-adopters; X is a vector of
factors influencing the decision to adopt. The sample
selection bias is what Heckman (1979) refers to as
the inverse Mill’s ratio (λ), is computed from the
parameter estimates of the selection equation for
each observation in the selected sample (Greene
1993), and is represented by:
(3)
Where and are respectively, the density and
distribution functions.
The level of adoption, Y
i
, specified in equation (4),
is observed only if
>0, and is estimated
by ordinary least squares, where the vector of
inverse Mill’s ratios is included as an additional
regressor in order to correct for potential selection
bias.
(4)
Y= proportion of area under improved rice variety.
The independent variables were as defined in the
selection model above.
Acknowledgement
Financial support by Africa Rice is gratefully acknowledged.
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