Jennifer,
Off the top of my head, it seems to me that, if degrees of freedom can
be considered roughly as the 'independent pieces of information' in the
model, I suppose that given the random choosing of your clusters
(villages), those 20 sub-groups are your only independent pieces of
information in your sample, and anything selected out of that
(sub-villages, then households) would be related, as they are in the
same cluster or PSU.
BUT, given the further sampling of households out of 'sub-villages' -
isn't this multi-stage sampling? Stata can handle that as well, I
believe, although I haven't had cause to use it (yet). I am not sure
how that would affect the degrees of freedom as Stata calculates it.
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Jennifer
Schmitt
Sent: September 3, 2009 1:48 PM
To: [email protected]
Subject: Re: st: RE: Survey design degrees of freedom help
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.
[email protected] wrote:
> Your degrees of freedom are 16??
> What is your sample size?
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Jennifer
> Schmitt
> Sent: September 3, 2009 11:26 AM
> To: [email protected]
> 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
[email protected]
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