This is a Stata specific question, and may be better directed to Stata's own Statalist, but I'm trying here first.
Here is the situation. I have a multiply-imputed data set, where the number of imputations = 10 and where imputations are only performed on independent variables. I would like to run the heckman
command on these data, using the mi estimate
prefix. The heckman
command is not a "supported command", but it is possible to force estimation using the cmdok
option. My questions are these: Why isn't heckman
a supported command? Are the results that I get when I force Stata to fit the model (using the cmdok
option) valid? Or, is there some statistical reason why a Heckman-style selection procedure should not be used in a multiply-imputed data setting?
Best Answer
I haven't used the
mi
command yet but I am using the user-written commandmim
in Stata for multiple imputed dataset. There are basically two issues in regard to your question. First, Rubin's method can be still used for the regression coefficients in the Heckman model as being used for linear regression. Second, marginal effects can be still combined as per Rubin's method as is mentioned here. As to why one need to invokecmdok
, Yulia Marchenko provides the following reasons (details here in Statalist)Commands are officially supported by
mi estimate
if they1) produce the numerical results that
mi estimate
needs and stores them wheremi estimate
expects (explained below)2) work properly with available
mi estimate
postestimation tools, and3) produce good-looking
mi estimate
output.