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# Re: st: ratio of 2 different surveys estimates? svyset , suest , fpc , nlcom

 From Steven Samuels To statalist@hsphsun2.harvard.edu Subject Re: st: ratio of 2 different surveys estimates? svyset , suest , fpc , nlcom Date Thu, 20 Jan 2011 14:15:42 -0500

```Austin--

```
I agree that the interpretation of statistics in the total population is not easy. I recall that you once suggested that the unit for repeated surveys of the same population should be something like a person-year. However Roman seems to be interested in estimating year- to-year differences (or ratios), so, for his purposes, the definition of the total population might not be an issue.
```

```
The -svyset- statement that I wrote assumes that, aside from certainty PSUs, a new sample of PSUs was drawn in each year. If this is not correct, then a different -svyset- statement is needed.
```
```
Roman, I'd like to know why fpc's varied greatly and how they were computed. If the survey had several stages and you are interested in primarily descriptive statistics, then perhaps the -svyset- should reflect the multi-stage structure.
```

Steve

On Jan 20, 2011, at 12:43 PM, Austin Nichols wrote:

Steve--
This works for inference on a population that is the sum of the
populations in each of two years--a strange population for many
purposes.

```
On Thu, Jan 20, 2011 at 9:00 AM, Steven Samuels <sjsamuels@gmail.com> wrote:
```
"Is this statistically correct..?"
Yes

Steve
sjsamuels@gmail.com

On Jan 20, 2011, at 4:03 AM, Roman Kasal wrote:

ok, I understand that, I already did this once, but is this
statistically correct adjusting=combine FPCs of two different surveys?
```
What if the FPCs are really very different (this is not mentioned case)?
```
-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Steven
Samuels
Sent: Wednesday, January 19, 2011 9:08 PM
To: statalist@hsphsun2.harvard.edu
```
Subject: Re: st: ratio of 2 different surveys estimates? svyset , suest
```, fpc , nlcom

Another way of putting this: When you combine independent surveys, you
must create a new stratum variable in which the individual original
strata in each survey appear. You would do this in your data, for
example by:
****************************
egen stratum =group(year stk)
*****************************
If there were 10 strata in 2006 and 10 in 2007, the new stratum
variable should have 20 levels. Then a single -svyset- statement will
allow joint analysis of the two surveys, as in my example.

Steve
sjsamuels@gmail.com
```
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