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List:       r-sig-robust
Subject:    Re: [RsR] Robust ANOVA with no interaction
From:       Rand R Wilcox <rwilcox () usc ! edu>
Date:       2015-03-03 21:00:29
Message-ID: 1425416428660.95182 () usc ! edu
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There is a paper regarding the strategy of testing for no interaction and using an \
additive model if the hypothesis of no interaction is not rejected:

Fabian, V. (1991). On the problem of interactions in the analysis of variance.
  Journal of the American Statistical Association, 86, 362--367.

The conclusion is that this strategy is not recommended roughly because it is unclear \
when power is sufficient high to justify using an additive model. 

For this reason, a method assuming an additive model has not been added to WRS2. If \
despite the results in Fabian there is some reason to include a function for an \
additive model, let me know and one will be added.

Best,

Rand

Rand Wilcox
Professor
University of Southern California
3620 McClintock Ave
Los Angeles, CA  90089-1061

Access to some reprints:
http://www.tandfonline.com/eprint/ypyq8ZKENfFXERFghYq7/full

________________________________________
From: R-SIG-Robust <r-sig-robust-bounces@r-project.org> on behalf of Worthington, \
                Thomas A <thomas.worthington@okstate.edu>
Sent: Tuesday, March 3, 2015 12:45 PM
To: r-sig-robust@r-project.org
Subject: [RsR] Robust ANOVA with no interaction

Dear All

We are trying to use the WRS2 package to run a robust ANOVA but am having some issues \
with model specification

The dependent variable is velocity and the predictors are temperature (Temp) and \
total suspended solids (TSS).  We would like to run a 2-way robust ANOVA using \
't2way' however one of the groups of the interaction is missing. We therefore ran a \
1-way robust ANOVA using the dummy variable Temp_TSS e.g.

t1waybt(Velocity ~ Temp_TSS, data=data, tr=0.2, nboot=10000)

The result suggested that the interaction was not significant . Therefore we would \
like to run a robust ANOVA with both main effects but no interaction (due to the \
missing group). We tried

t1waybt(Velocity ~ TSS + Temp, data=data, tr=0.2, nboot=10000)

but this only tests for first variable stated (in this case TSS). Is this possible to \
run an ANOVA with just the main effects but no interaction?

Thanks
Tom

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