Hello, This one is very perplexing. I have teacher observation data,
with factors teacher ID, observer ID, component, grade and subject. When
I do this,
aov(data=ratings.prin.22, rating ~ obsid.f + tid.f + subject.f + grade.f +
comp.f)
I get this:
Terms:
obsid.f tid.f grade.f comp.f Residuals
Sum of Squares 306.23399 221.38173 1.70000 14.52831 279.05780
Deg. of Freedom 74 87 2 9 1406
This looks right. There are about 82 observers so 74 degrees of freedom
for obsid.f is OK. But if I do this (just reordering the terms in the
formula):
aov(data=ratings.prin.22, rating ~ comp.f + grade.f + subject.f + tid.f +
obsid.f)
I get this:
Terms:
comp.f grade.f subject.f tid.f obsid.f Residuals
Sum of Squares 15.0923 23.3968 5.9982 499.3568 0.0000 279.0578
Deg. of Freedom 9 4 4 152 3 1406
Now obsid.f only has 3 degrees of freedom and the sum of squares is
0.00. Could this be due to the unbalanced design?
If someone can explain this to me I would be very grateful.
--
Stuart Luppescu -=- slu .at. ccsr.uchicago.edu
University of Chicago -=- CCSR
???????? -=- Kernel 3.2.1-gentoo-r2
Tony Plate: There looks to be a typo in the R-exts
manual: [...] Peter Dalgaard: 'svn blame' tells me
that this was Brian's addition in rev.35362 [...]
Brian D. Ripley: I prefer 'svn praise' myself.
Peter Dalgaard: Or 'svn annotate'. I think it
depends on what I'm looking for, plus the risk
that the author (perpetrator, contributor) might
be me... -- Tony Plate, Peter Dalgaard and
Brian D. Ripley (about a typo in the
Hi, It seems that you have an unbalanced anova case which can be complicated in interpretation. This question has been addressed in the list you can search of previous mails. Basically, for unbalanced data (or unorthorgonal), estimates of SS of a factor depends on other factors. Type I SS (which is the method by aov) is a sequential method. Therefore, order of variables in the model matters. For your situation, you may want to use type II or type III SS (check Anova in car) because they are estimates adjusted for other variables in the model, thus order-independent. Weidong Gu On Thu, Mar 22, 2012 at 5:06 PM, Stuart Luppescu <slu at ccsr.uchicago.edu> wrote:> Hello, This one is very perplexing. I have teacher observation data, > with factors teacher ID, observer ID, component, grade and subject. When > I do this, > > aov(data=ratings.prin.22, rating ~ obsid.f + tid.f + subject.f + grade.f + comp.f) > > I get this: > > Terms: > ? ? ? ? ? ? ? ? ?obsid.f ? ? tid.f ? grade.f ? ?comp.f Residuals > Sum of Squares ?306.23399 221.38173 ? 1.70000 ?14.52831 279.05780 > Deg. of Freedom ? ? ? ?74 ? ? ? ?87 ? ? ? ? 2 ? ? ? ? 9 ? ? ?1406 > > This looks right. There are about 82 observers so 74 degrees of freedom > for obsid.f is OK. But if I do this (just reordering the terms in the > formula): > > aov(data=ratings.prin.22, rating ~ comp.f + grade.f + subject.f + tid.f + obsid.f) > > I get this: > > Terms: > ? ? ? ? ? ? ? ? ?comp.f ?grade.f subject.f ? ?tid.f ?obsid.f Residuals > Sum of Squares ? 15.0923 ?23.3968 ? ?5.9982 499.3568 ? 0.0000 ?279.0578 > Deg. of Freedom ? ? ? ?9 ? ? ? ?4 ? ? ? ? 4 ? ? ?152 ? ? ? ?3 ? ? ?1406 > > Now obsid.f only has 3 degrees of freedom and the sum of squares is > 0.00. Could this be due to the unbalanced design? > > If someone can explain this to me I would be very grateful. > > -- > Stuart Luppescu -=- slu .at. ccsr.uchicago.edu > University of Chicago -=- CCSR > ???????? -=- ? ?Kernel 3.2.1-gentoo-r2 > Tony Plate: There looks to be a typo in the R-exts > ?manual: [...] Peter Dalgaard: 'svn blame' tells me > ?that this was Brian's addition in rev.35362 [...] > ?Brian D. Ripley: I prefer 'svn praise' myself. > ?Peter Dalgaard: Or 'svn annotate'. I think it > ?depends on what I'm looking for, plus the risk > ?that the author (perpetrator, contributor) might > ?be me... ? ?-- Tony Plate, Peter Dalgaard and > ?Brian D. Ripley (about a typo in the > > ______________________________________________ > R-help at 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.
On Mar 22, 2012, at 5:06 PM, Stuart Luppescu wrote:> Hello, This one is very perplexing. I have teacher observation data, > with factors teacher ID, observer ID, component, grade and subject. > When > I do this, > > aov(data=ratings.prin.22, rating ~ obsid.f + tid.f + subject.f + > grade.f + comp.f) > > I get this: > > Terms: > obsid.f tid.f grade.f comp.f Residuals > Sum of Squares 306.23399 221.38173 1.70000 14.52831 279.05780 > Deg. of Freedom 74 87 2 9 1406 > > This looks right.What about the missing SS for subject.f?> There are about 82 observers so 74 degrees of freedom > for obsid.f is OK. But if I do this (just reordering the terms in the > formula): > > aov(data=ratings.prin.22, rating ~ comp.f + grade.f + subject.f + > tid.f + obsid.f) > > I get this: > > Terms: > comp.f grade.f subject.f tid.f obsid.f Residuals > Sum of Squares 15.0923 23.3968 5.9982 499.3568 0.0000 > 279.0578 > Deg. of Freedom 9 4 4 152 3 > 1406 > > Now obsid.f only has 3 degrees of freedom and the sum of squares is > 0.00. Could this be due to the unbalanced design?I would have guessed collinearity.> > If someone can explain this to me I would be very grateful. > > -- > Stuart Luppescu -=- slu .at. ccsr.uchicago.eduDavid Winsemius, MD West Hartford, CT