[R] anova and lm results differ

[Prof Brian Ripley]

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.lamprianou at manchester.ac.uk

-- 
Brian D. Ripley,                  ripley at 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