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st: RE: Heckman Selection Model: How to deal with missing observations?

From   "Nick Cox" <>
To   <>
Subject   st: RE: Heckman Selection Model: How to deal with missing observations?
Date   Thu, 17 Feb 2005 22:45:59 -0000

I don't think it makes much difference what 
your models are. You have a choice with missing
data between living with them and using some 
method to impute non-missing values, after 
which your model may show improved performance, 
but you should worry how genuine that improvement 
might be. Thus neither approach is problem-free, 
but there is an enormous literature on the matter 
and some Stata implementations of imputation methods, 
among which -impute-, -hotdeck- and -mice- spring to mind. 
-findit- will give further pointers. 


Quang Nguyen
> I am applying the Heckman procedure to estimate the role of "Share
> Contract" in longline fishery. In the first step, I run a Probit model
> where the dependent variable is the binary variable "Share Contract or
> something else", the independent variables include  economic factors
> such as variable cost, risk sharing attitude...  In the second step, I
> run OLS where dependent variable is revenue and several independent
> variables including the binary variable "Share Contract...". My data
> includes about 95 observations.
> After running the Heckman procedures, no variable seems statisitically
> significant. Some coeficinces have unxpected sign. I think one of the
> reason is probably due to many missing observations. Or it could be
> some other reasons.
> I would highly appreciate if anyone could help me to fin dthe way
> dealing with this matter, especially with respect to missing
> observations. Also, any idea on how to improve the model would be very
> much appreciated.

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