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Re: st: RE: non-constant Frequency weights


From   Stephen O Neill <stepheno_neill_1999@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: non-constant Frequency weights
Date   Tue, 26 Oct 2010 14:01:01 -0700 (PDT)

Thats great - thank you very much for your help Steve - I really appreciate it.

Stephen


----- Original Message ----
From: Steven Samuels <sjsamuels@gmail.com>
To: statalist@hsphsun2.harvard.edu
Sent: Tue, October 26, 2010 9:56:34 PM
Subject: Re: st: RE: non-constant Frequency weights

--

Thanks, Stephen.

To answer your question: If the panels is based ona sample of the population in 
the first year, then use that first year weight.  If the panel is a rotating 
panel, with individuals entering in different years, than for those individuals, 
use the weight for their first year.  The weights in different years are useful 
for presenting cross-sectional statistics for each of the years, but not for the 
panel analysis.

Also, the weights should not be specified as probability weights, not frequency 
weights.  A frequency weight equal to K, say, is intended for use when there are 
K individuals in the _sample_  with identical values.  If you tell a commandthat 
the weights are frequency weight, then you are saying that the sample size is 
equal to the population size.

Regards,

Steve

Steven J. Samuels
sjsamuels@gmail.com
18 Cantine's Island
Saugerties NY 12477
USA
Voice: 845-246-0774
Fax:    206-202-4783


On Oct 26, 2010, at 4:34 PM, Stephen O Neill wrote:

Hi Steve,
My data is from a survey which contains weights representing the number of
inidividuals in the population represented by each sample observation. However
in differnt years this frequency weight is different i.e. the number of
population individuals the sample observation represents changes from year to
year.
Hope this clarifies,
Stephen



----- Original Message ----
From: Steven Samuels <sjsamuels@gmail.com>
To: statalist@hsphsun2.harvard.edu
Sent: Tue, October 26, 2010 7:40:47 PM
Subject: Re: st: RE: non-constant Frequency weights


Stephen O Neill:

Off-topic, but I'm curious:  How can you have repeated identical observations on
one individual at a single time point, which is what a frequency weight>1 would
imply?

Steve
sjsamuels@gmail.com


On Oct 26, 2010, at 2:28 PM, Nick Cox wrote:

Fair enough. Now you have a specific question, to which I don't know the answer;
but someone else may have specific advice.

Nick
n.j.cox@durham.ac.uk

Stephen O Neill

When I try to run - xtreg,fe - I get the error message "weight must be constant
within ID", where ID is my unique identifier for each individual and is constant
for an individual over time. I also wanteed to use the user written - xtabond2 -
or some other dynamic model but it appears that weights can't be used with
these.

Nick Cox <n.j.cox@durham.ac.uk>

I don't see the connections between these statements. A variable containing
frequency weights can vary between observations, in this instance within panels
as well as between panels, so that is not a problem in itself.

Perhaps some particular procedures have more restricted assumptions, but you
don't say what they are.

Stephen O Neill

I am using unbalanced panel data which contains a frequency weight each year.
However the weight is not constant through time with the result that I cannot
weight the data using - [fweight = weight] - . I was just wondering if there is
a simple work around?


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