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From | Nick Cox <njcoxstata@gmail.com> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: means compairison with weights and unequal variance |
Date | Sun, 20 Nov 2011 11:02:25 +0000 |
You may be better off analysing your outcome variable on a transformed scale, either directly or using a link function through -glm-. -glm- can use aweights. Note also the possibility of -regress outcome treatvar- with aweights. You seem to be relying on significance test results to tell you about basic characteristics of your data. Something like -dotplot outcome treatvar- would be a useful supplement. Nick Barbro Widerstedt [edited to use Statalist conventions] > I have a dataset where I try to compare the means of a variable > between two groups (treated and untreated). > The data set used is a sample, drawn from the superpopulation by the > ado-package -cem- (Iaucus et al Coarsened enhanced matching), and > subsequent estimations should be weighted. > > This means that a standard t-test cannot be used, and I searched a bit > and found that -oneway- is an alternative with weighted data. However, > the groups have unequal variance which is a problem for -oneway- (at > least I think so, I know ANOVA mainly by name ...). I read one entry > that suggests that -oneway- is robust to groupwise unequal variance if > groupsize does not vary too much, but in my case they do (min > groupsize=2 max groupsize=1273) > > ttest <outcome>, by(treatvar) unequal -> t = -2.43 > oneway <outcome> <treatvar> [aweight=cem_weight] -> F=4.06 > > Both Bartlett's test for equality of variance, a standard -sdtest- , > and -robvar- suggest that I have unequal variance between groups. > > Suggestions of alternatives would be greatly appreciated * * 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/