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Re: st: Re: RE: when your sample is the entire population


From   "Michael Blasnik" <[email protected]>
To   <[email protected]>
Subject   Re: st: Re: RE: when your sample is the entire population
Date   Fri, 18 Jan 2008 23:09:46 -0500

Absolutely -- that issue is often the major issue in program evaluations. I hope I didn't imply anything else.

Michael

----- Original Message ----- From: "David Greenberg" <[email protected]>
To: <[email protected]>
Sent: Friday, January 18, 2008 7:08 PM
Subject: Re: st: Re: RE: when your sample is the entire population



Michael, while it is true that program participants or school children could be considered a sample of a larger population, people are not usually in treatment programs or in particular schools at random, and the choice of institutions to study - this school rather than that school - are often not made at random either. So, one may have a sample but ordinarily not a simple random sample. Without taking selection effects into account, generalization to a larger population could be quite treacherous. David Greenberg, Sociology Department, New York University

----- Original Message -----
From: Michael Blasnik <[email protected]>
Date: Friday, January 18, 2008 4:32 pm
Subject: st: Re: RE: when your sample is the entire population
To: [email protected]



I would just say -- "what Nick says" ;)

But I'd like to emphasize one aspect related to his points 3 (and/or
4) --
measurement error.  In many real applications, the outcome (and,
unfortunately,
the predictors) are measured with error.  Therefore, you have
uncertainty even
with data for the full population.  Also, the superpopulation concept
( point 1)
seems quite reasonable -- at least for most program evaluation
questions where
you may collect data for all program participants (or kids in a
school) but they
can be considered a sample of some larger potential population.  Of
course in
program evaluation you also still have uncertainty introduced by any
comparison/control group employed in the analysis.

Michael Blasnik
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