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Re: st: RE: Survey design degrees of freedom help


From   Jennifer Schmitt <jorg0206@umn.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: Survey design degrees of freedom help
Date   Thu, 03 Sep 2009 12:48:17 -0500

My sample size is 489, but I only have 20 PSU, 3 Strata so my design df = 20-3-1 (for the constant). I have a stratified, clustered sample and so my design df are based off my PSU and are thus really low. I just do not know know why this is the case (I have accepted that it is the case), but I can't defend that without knowing why (or maybe it is wrong, but everything in the FAQ and help sections online suggest it is correct). Thanks.

Andrew.Clapson@statcan.gc.ca wrote:
Your degrees of freedom are 16??
What is your sample size?

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Jennifer
Schmitt
Sent: September 3, 2009 11:26 AM
To: statalist@hsphsun2.harvard.edu
Subject: st: Survey design degrees of freedom help


Hello everyone,
I need some important clarification about the design degrees of freedom for stratified clustered survey analysis. I have data that was stratified by three areas (NW, SW, and E). We randomly chose villages from these three areas, then chose 5 subvillages within the village and within the subvillage we chose households (the unit of interest for my analysis). I am running logistic regressions with PSU = village, strata

= area and probability weights. My design degrees of freedom are 16 (PSU-strata-one for the constant term). I get that. What I do not understand is WHY and how to explain to others unfamiliar with STATA that it is correct, any answers to this would be greatly appreciated. The reason this is an issue is that I want to test more than 16 variables at once and obviously I can't with only 16 df. Thank you.
Jennifer


--
Jennifer Schmitt
PhD Candidate - Conservation Biology Program
jorg0206@umn.edu

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