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From |
Steven Samuels <[email protected]> |

To |
[email protected] |

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

Date |
Thu, 11 Sep 2008 07:16:20 -0400 |

You are welcome, hafida. Looking over your post again, I saw that you were concerned about Normality. A Normal distribution for the error terms is not a needed assumption of survey regression commands, (nor of OLS, either, except to create prediction intervals). I have often run -svy: reg- on discrete outcomes. What you do need is a correct model for the mean.

-Steve

On Sep 11, 2008, at 5:10 AM, [email protected] wrote:

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 <[email protected]>

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, [email protected] 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 ofthemhave skewed distributions. I originally intended to use --manova&--mvreg until lately when I realised that I'm using a datasetfroma survey with over-sampling for participants living in remote areas. The dataset had had a weighted variable already so have totake 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 onhowto apply --svy nor --pw to --manova and --mvreg. Some of my concerns are: a. I need descriptives other than mean & proportion, particularlyfor skewed DVs which I think median or percentiles is more appropriate. While --svy does not support this, is there a way toget the estimates? b. How to create histogram for weighted mean DV as this will helpget a sense if assumption for normality for an OLS regression ismet?> c. When using --regress with --svy to get ANOVA, how is homogeneityof 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 possibletorun --mvreg and take weights into account?* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: Trend Test for Rates***From:*[email protected]

**st: --svy & --pweights: problems for median, graphs & regression***From:*[email protected]

**Re: st: --svy & --pweights: problems for median, graphs & regression***From:*Steven Samuels <[email protected]>

**Re: st: --svy & --pweights: problems for median, graphs & regression***From:*[email protected]

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