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Re: st: problems with e(sample)


From   Richard Williams <Richard.A.Williams.5@ND.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: problems with e(sample)
Date   Fri, 16 Jun 2006 23:21:45 -0500

At 05:33 PM 6/16/2006, Zurab Sajaia wrote:
I found the cause of problem, -restore- works after setting all the ereturns and it clears e(sample) leaving other parameters unchanged.

"esample(varname) specified with ereturn post or repost gives the name of the 0/1 variable indicating the observations involved in the estimation.
The variable is removed from the data but is available for use as
e(sample);"

This is what they say in the help so it's still unclear to me why e(sample) disapeares after restoring original data...
I am not sure how e(sample) works but I have always suspected it is really a variable masquerading as a function. If not, it must contain all the rules that would be needed to create such a variable. In any event, it seems to behave pretty much the same way as a variable - restore the data to an earlier point and variables created since then (along with e(sample)) get lost too.

I can see why it would be difficult to keep e(sample) alive after doing a restore. Suppose I preserved the data, then did a collapse, then did a restore. What is e(sample) supposed to identify as 0 and 1? Or, suppose I preserved, gave various commands that deleted or added cases, ran my command, and then restored. How would e(sample) keep track of all the data commands that occurred before I ran my estimation command? Or, how about preserve, reshape, restore?

I suppose if you really wanted/needed to keep e(sample) alive, you could create and save a new dataset before you did you restore, and then merge your original data set with the one that contained e(sample). Alternatively, I suppose it wouldn't be too hard to figure out the commands that would generate e(sample) if you didn't already have it.


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Richard Williams, Notre Dame Dept of Sociology
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