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

From   Steven Samuels <>
Subject   Re: st: ratio of 2 different surveys estimates? svyset , suest , fpc , nlcom
Date   Thu, 20 Jan 2011 14:15:42 -0500


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.


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

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

On Thu, Jan 20, 2011 at 9:00 AM, Steven Samuels <> wrote:

"Is this statistically correct..?"


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-----
[] On Behalf Of Steven
Sent: Wednesday, January 19, 2011 9:08 PM
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.

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