Dear Statalist:
I am trying to run a Heckman correction on a panel data set that has a significant amount of attrition in the data as there are numerous new firms that drop out during the 8 year time period. When I run heckman, I notice that the number of unobserved to be used in heckman is much smaller (13) as shown below.
Heckman selection model Number of obs = 7637
(regression model with sample selection) Censored obs = 13
Uncensored obs = 7624
Wald chi2(6) = 731.45
Log likelihood = -82337.21 Prob > chi2 = 0.0000
My data set is such that when a firm drops out, there are no subsequent years entered for that firm. Do I need to have a year for each firm even if they drop out and just enter zeros for the dependent and independent variables?
Is there a way to go through and add observations easily?
Thanks for any advice!
Steve
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