[Limdep Nlogit List] Error 127: Models - Sample sum of weights is less than or equal to 1.0

[Vrachioli,Maria]

Hello,


I am using NLOGIT's usual format for sample selection models PROBIT and FRONTIER command.

While this model is working for the pooled data (N=265) and treated farmers data (N=231), it gives me the following error

when I am trying to run this model using the control group of farmers (N=31):


|-> FRONTIER ; Lhs = loutput ; Rhs = one,lcapital,llabour,lland ; Selection $
Error    127: Models - Sample sum of weights is less than or equal to 1.0
(it gives me the same error using or not Halton for the simulation)

I do not know how to interpret this error and what it would solve this issue.

My command for the sample selection model for the control group is the following:

PROBIT ; Lhs = extension ; Rhs = one,age,age2,educ,educ2,subsidies,tenancy,aridity,altitude ; Hold $
FRONTIER ; Lhs = loutput ; Rhs = one,lcapital,llabour,lland ; Selection $
                    ; Halton ; Draws = 100 $

I am using a Cobb-Douglas production function with only 3 inputs, as I know that my data set for the control group is relatively small.

I would like to thank you in advance for your help.

Best regards,
Maria