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


From   Steven Samuels <sjhsamuels@earthlink.net>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: --svy & --pweights: problems for median, graphs & regression
Date   Thu, 11 Sep 2008 03:07:53 -0400

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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