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

[Steven Samuels <sjhsamuels@earthlink.net>]

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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