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st: How to skip logit when there is no variation in the dependentvariable


From   Thomas de Hoop <T.deHoop@maw.ru.nl>
To   statalist@hsphsun2.harvard.edu
Subject   st: How to skip logit when there is no variation in the dependentvariable
Date   Mon, 19 Mar 2007 11:10:39 +0100

Dear Statalist users,

I have created dummy variables for 214 countries. For each of these countries I want to estimate several logit models to estimate chances of certain situations to occur, and create chance variables from the prediction of these models. I estimate these chances using data from the past. I have data of these situation For this I created loops with the foreach and forvalue commands from stata. The problem is that in some countries a certain situation never occurred. For these situations there are only 0 value observations. Of course logistic regression is not possible in these kind of situations. For this reason I would like to skip these equations in the loop.
For this reason I counted the number of times a situation did occur in the past and created a variable.

I tried to skip the equation as follows:

forval i=1/214 {
logit drought`i' variable1 variable 2 etc. if droughtcount`i'>0
}

i= the country number
variable1 variable2 etc are the explanatory variables.

drought`i'=the situation in a certain country
droughtcount`i'=the number of times a situation did occur in the past.

For country 3 this results in the following error:
no observations
r(2000);

How can I prevent this error?

Best regards,

Thomas de Hoop





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