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# Re: st: RE: non-constant Frequency weights

 From Steven Samuels To statalist@hsphsun2.harvard.edu Subject Re: st: RE: non-constant Frequency weights Date Tue, 26 Oct 2010 16:56:34 -0400

```--

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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