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Re: st: --svy & --pweights: problems for median, graphs & regression


From   Nur.Hikmayani@studentmail.newcastle.edu.au
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: --svy & --pweights: problems for median, graphs & regression
Date   Thu, 11 Sep 2008 16:10:36 +0700

Thanks heaps, Steve! 
Also for correcting the way I wrote commands...

hafida--




Nur Hafidha Hikmayani
School of Medicine & Public Health
The University of Newcastle
Australia




----- Original Message -----
From: Steven Samuels <sjhsamuels@earthlink.net>
Date: Thursday, September 11, 2008 2:07 pm
Subject: Re: st: --svy & --pweights: problems for median, graphs & regression

> Hafida
> 
> 
> 
> a. Look at -help-   for -pctile- and -_pctile-.  These take pweights
> 
> b. -histogram- will take fweights, but not pweights: See http:// 
> www.stata.com/statalist/archive/2007-10/msg00327.html and preceding 
> 
> messages in the thread.
> 
> c. -svy: reg- automatically computes standard errors that are 
> robust  
> to heteroskedasticity. Homogeneity of variance is not an assumption 
> 
> for survey tests of means or regression coefficients.
> 
> d.  See: http://www.stata.com/statalist/archive/2007-
> 12/msg00621.html  
> to compute an adjusted R-square with survey data.  You should  
> consider other measures of fit, such as -linktest-.
> 
> e.  No--not if you want to believe the standard errors and tests.   
> However you might be able to test hypotheses about single-outcome  
> survey regressions with -suest-.
> 
> To use the survey-enabled programs like -svy: reg-  for inference  
> (hypothesis, confidence intervals, standard errors) you must first -
> 
> svyset- your data.  -svyset- will allow you to account for the 
> entire  
> sampling design, not just weighting.
> 
> 
> For future reference the appropriate way to refer to Stata commands 
> 
> in the list is with hyphens around them"  "-manova-" , not "--manova"
> 
> 
> -Steve
> 
> On Sep 11, 2008, at 12:59 AM,  
> Nur.Hikmayani@studentmail.newcastle.edu.au wrote:
> 
> > Hi all,
> >
> > I have 4 continuous DVs (quality of life domains of SF-36: GH, 
> PF,  
> > MH, SF) which are moderately inter-correlated (0.5) and two of 
> them  
> > have skewed distributions. I originally intended to use --manova 
> &  
> > --mvreg until lately when I realised that I'm using a dataset 
> from  
> > a survey with over-sampling for participants living in remote  
> > areas. The dataset had had a weighted variable already so have to 
> 
> > take this into account. To some extent, this had affected the  
> > statistical method I'd like to use previously. So far, I've  
> > performed a separate analysis for each DV as I have no idea on 
> how  
> > to apply --svy nor --pw to --manova and --mvreg.
> >
> > Some of my concerns are:
> > a. I need descriptives other than mean & proportion, particularly 
> 
> > for skewed DVs which I think median or percentiles is more  
> > appropriate. While --svy does not support this, is there a way to 
> 
> > get the estimates?
> > b. How to create histogram for weighted mean DV as this will help 
> 
> > get a sense if assumption for normality for an OLS regression is 
> met?> c. When using --regress with --svy to get ANOVA, how is 
> homogeneity  
> > of variance assessed?
> > d. I noticed that there is no adjusted R-squared when using --
> svy,  
> > so is it appropriate to build a model using R-squared instead?
> > e. Lastly, if it's not impractical at all, is it still possible 
> to  
> > run --mvreg and take weights into account?
> >
> *
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