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st: non parametric anova equivalent for factorial experiments?


From   "Armstrong, Alona" <alona.armstrong@lancaster.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: non parametric anova equivalent for factorial experiments?
Date   Thu, 4 Mar 2010 10:01:20 -0000

Hi,
I have undertaken two factorial experiments. One has 3 factors each with
2 levels and the other has two factors, one with 2 levels and the other
with 3. The data are balanced with 3 replicates. I have tested for
homogeneity of variances by Levenes and Hartleys Maximum F ratio and the
data fail. Much of this is caused by one factor producing more variable
data for one level compared with the other but there are also some
outliers (but I would prefer not to exclude them as this is
representative of what I am studying). So, I have been looking around
for some non-parametric alternatives to ANOVA that can handle a
factorial design but with limited success (I have tried a rank-anova
approach but the same problems persist and there seems to be some debate
about the validity of that approach). Does anyone have any suggestions
and know of any existing Stata code? Any thoughts, recommendations or
pointers would be greatly appreciated.
Regards,
Alona

Dr Alona Armstrong
PDRA
Lancaster Environment Centre
Lancaster University
Lancaster
LA1 4YQ





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