Dear useRs,
I would like to apply a nested ANOVA on my dataset, but I cannot find a
satisfying answer on how to implement it in R.
For example, fac2 is nested within fac1:
df <- data.frame(resp=rnorm(12), fac1=rep(LETTERS[1:2],each=6),
fac2=rep(letters[1:6],each=2))
I have found three different ways that are said to be nested designs and
I cannot understand whether they do the same or not. They all give
similar results with this example but it might not always be the case.
1) following:
http://www.personal.psu.edu/mar36/stat_461/nested/nested_designs.html
summary(aov(resp~fac1+fac1/fac2, data=df))
2) following:
http://www.zoology.unimelb.edu.au/stats/Worksheets/nested%20two-way%20anova%20curdies.pdf
summary(aov(resp~fac1+fac2%in%fac1, data=df))
This notation is very intuitive to me.
3) following:
http://cran.r-project.org/doc/contrib/Vikneswaran-ED_companion.pdf
summary(aov(resp~fac1+fac1:fac2, data=df))
For me, the ":" specifies the interaction. Is this then analogous since
in a nested design the levels of fac2 are different in each level of fac1?
So my questions are: Are there differences between these notations? If
yes, which ones? And then, which notation should I prefer?
And if they are identical, then why are there 3 (or more) ways to do it?
Is there a reason not to have a single implementation?
Thank you in advance,
Ivan
--
Ivan Calandra
University of Franche-Comté
Laboratoire Chrono-Environnement
Bureau ATER -107L
16, Route de Gray
25030 Besançon Cedex, France
ivan.calan...@univ-fcomte.fr
+33 (0) 381 66 20 60
http://chrono-environnement.univ-fcomte.fr/spip.php?article1830
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