Re: st: problems with e(sample)

[Richard Williams <Richard.A.Williams.5@ND.edu>]

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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