So, should I avoid using the Anova option of the Rcmdr and use aov instead (as I have been doing)?
Dr. Iasonas Lamprianou Assistant Professor (Educational Research and Evaluation) Department of Education Sciences European University-Cyprus P.O. Box 22006 1516 Nicosia Cyprus Tel.: +357-22-713178 Fax: +357-22-590539 Honorary Research Fellow Department of Education The University of Manchester Oxford Road, Manchester M13 9PL, UK Tel. 0044 161 275 3485 iasonas.lampria...@manchester.ac.uk --- On Tue, 31/8/10, Prof Brian Ripley <rip...@stats.ox.ac.uk> wrote: > From: Prof Brian Ripley <rip...@stats.ox.ac.uk> > Subject: Re: [R] anova and lm results differ > To: "Iasonas Lamprianou" <lampria...@yahoo.com> > Cc: r-help@r-project.org > Date: Tuesday, 31 August, 2010, 17:27 > You have confused 'Anova', 'aov' and > 'anova'. R has aov() and > anova(), package car (called from Rcmdr) has Anova(). > They are not > the same things: Anova computes (so-called, by SAS) > 'type-II or > type-III analysis-of-variance tables', something > deliberately not > available in base R. > > See http://www.stats.ox.ac.uk/pub/MASS3/Exegeses.pdf for > some > background and why many distinguished statisticians regard > your > example of the use of Anova() as meaningless. > > In any case, lm (in your subject line) is innocent ... it > does not > compute any form of ANOVA table. > > On Tue, 31 Aug 2010, Iasonas Lamprianou wrote: > > > Dear all > > > > I have found that the two "equivalent" commands do not > produce the same results. > > 1. (I wrote this command by hand, this is > what I would do usually) > > >summary(aov(eduyrs ~ cntry * edf, > data=ESS1)) > > > Df Sum Sq Mean Sq F value > Pr(>F) > > cntry > 1 257 256.65 21.2251 4.243e-06 *** > > edf > 4 11010 2752.42 227.6296 < 2.2e-16 *** > > cntry:edf 4 > 24 > 6.03 0.4987 0.7367 > > Residuals 3205 > 38754 12.09 > > --- > > Signif. codes: 0 '***' 0.001 '**' > 0.01 '*' 0.05 '.' 0.1 ' ' 1 > > > > 2. (I run this from Rcmdr, this is what my students > would normally do) > > >AnovaModel.2 <- (lm(eduyrs ~ > cntry*edf, data=ESS1)) > > > Anova(AnovaModel.2) > > Anova Table (Type II tests) > > Response: eduyrs > > Sum > Sq Df F value Pr(>F) > > cntry > 38 1 3.1158 > 0.07763 . > > edf > 11010 4 227.6296 < 2e-16 *** > > cntry:edf > 24 4 0.4987 > 0.73672 > > Residuals 38754 3205 > > --- > > Signif. codes: 0 '***' 0.001 '**' > 0.01 '*' 0.05 '.' 0.1 ' ' 1 > > > > Unfortunately, the results are different. > Could anyone, please, explain why? > > > > > > Dr. Iasonas Lamprianou > > > > > > Assistant Professor (Educational Research and > Evaluation) > > Department of Education Sciences > > European University-Cyprus > > P.O. Box 22006 > > 1516 Nicosia > > Cyprus > > Tel.: +357-22-713178 > > Fax: +357-22-590539 > > > > > > Honorary Research Fellow > > Department of Education > > The University of Manchester > > Oxford Road, Manchester M13 9PL, UK > > Tel. 0044 161 275 3485 > > iasonas.lampria...@manchester.ac.uk > > -- > Brian D. Ripley, > rip...@stats.ox.ac.uk > Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ > University of Oxford, > Tel: +44 1865 272861 (self) > 1 South Parks Road, > +44 1865 > 272866 (PA) > Oxford OX1 3TG, UK > Fax: +44 1865 272595 > ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
