Dear Stata listers,

I am estimating a model with a dependent truncated variable (i.e. an index between 0 and 1: "INDEX"), a bivariate endogenous variable ("END") instrumented by another bivariate variable ("Z") and a list of exogenous variables, X1…X5 . In order to avoid the forbidden regression of a 2SLS estimate (first stage probit, second stage tobit), I tried to use the cmp command as follows:

cmp (INDEX = X1 X2 X3 X4 X5 ENDO) (ENDO = Z X1 X2 X3 X4 X5) , ind ("cond(INDEX>0, cond(INDEX <1, $cmp_cont, $cmp_right), $cmp_left )" $cmp_probit) robust

Is that correct? Does this procedure avoid the forbidden regression?


Or do I need to use the suffix # as in the following?

cmp (INDEX = X1 X2 X3 X4 X5 ENDO#) (ENDO = Z X1 X2 X3 X4 X5), ind ("cond(INDEX>0, cond(INDEX <1, $cmp_cont, $cmp_right), $cmp_left )" $cmp_probit) robust

Thanks in advance,

Elisa