Re: st: Kruskal-Wallis equivalent for survey data with pweight

[Steven Samuels <sjhsamuels@earthlink.net>]

--

You have not given us a good reason for preferring the K-W test. It  
is the most widely known rank test for comparing >2 groups, but there  
are many others.   The test from -stcox- is appropriate for any  
positive random variable, censored or not. It has power to detect  
group differences even if the proportional-hazards assumption is  
false.  You report the p-value from the test statistic, but you need  
not report estimated coefficients-these depend on the truth of the  
proportional-hazards assumption.  Instead, plot the weighted survival  
or distribution curves.

However, a k-sample test is rarely enough by itself, even if  
"significant".  The real questions are: which groups differ from one  
another? how do they differ? are the differences explained or  
moderated by other factors?

Good luck!

Steve


On Nov 1, 2008, at 7:12 AM, Aca N.T. wrote:

> Thanks Maarten & Steven, I have to change the analyses for LOS.
> However, I've picked a wrong example here since I have some other
> skewed variables for which KW test remains appropriate I think (eg.
> triglyceride level). Can you suggest how to perform the analysis using
> Stata?
>
> Thanks in advance.
> Aca
>
> On Fri, Oct 31, 2008 at 4:24 PM, Maarten buis  
> <maartenbuis@yahoo.co.uk> wrote:
> > --- "Aca N.T." <acant29@gmail.com> wrote:
> > > I have a simple question about testing length of stay (LOS)
> > > differences among 5 groups. The response variable (LOS) has a skewed
> > > distribution. I have previously transformed the LOS (log
> > > transformation) and tried parametric statistic (ANOVA using
> > > svy:regress), but not happy when performing back-transformation for
> > > SD/SE. I rarely used non-parametric statistics before even for
> > > non-survey data, so really this issue is a hassle for me. I believe,
> > > however, that Stata has a test equivalent to Kruskal-Wallis for
> > > survey data.
> >
> > The conventional way of analysing length of stay data is using  
> > survival
> > analysis. So I would -stset- the data, and than use -sts test- to do
> > the test. You can specify weights in the -stset- command. See:
> > -help stset- and -help -sts test-.
> >
> > Hope this helps,
> > Maarten
> >
> >
> >
> >
> >
> > -----------------------------------------
> > Maarten L. Buis
> > Department of Social Research Methodology
> > Vrije Universiteit Amsterdam
> > Boelelaan 1081
> > 1081 HV Amsterdam
> > The Netherlands
> >
> > visiting address:
> > Buitenveldertselaan 3 (Metropolitan), room N515
> >
> > +31 20 5986715
> >
> > http://home.fsw.vu.nl/m.buis/
> > -----------------------------------------
> >
> >
> >
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