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


From   Quang Nguyen <quangn@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Heckman Selection Model: How to deal with missing observations?
Date   Thu, 17 Feb 2005 12:01:07 -1000

Dear All, 

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.

Have A Wonderful Day!
Quang
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