Dear Mario, When there are empty cells, some of the usual contrasts defining interactions (and possibly even main effects) can't be estimated, and one should be especially careful about what hypotheses are being tested. There's a good introduction to these problems (in my opinion) by Searle, Speed, and Henderson in The American Statistician, Vol. 35, No. 1. (Feb., 1981), pp. 16-33. The issues are sufficiently complex that I thought it inadvisable to provide an automatic solution.
For the data pattern that you give, you could test the hypothesis of no interaction via anova(lm(y ~ a + b), lm(y ~ a*b)). If the interaction seems negligible, you could test the main effects via Anova(lm(y ~ a + b), error=lm(y ~ a*b)). I hope this helps, John -------------------------------- John Fox Department of Sociology McMaster University Hamilton, Ontario Canada L8S 4M4 905-525-9140x23604 http://socserv.mcmaster.ca/jfox -------------------------------- > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Mario Morales > Sent: Tuesday, April 11, 2006 12:05 PM > To: [email protected] > Subject: [R] type II and III Sum square whit empty cells > > Dear all > > I need to run an anova from a factorial model > > y_{ijk}=\alpha_i+\beta_j+(\alpha\beta)_{ij}+e_{ijk} > > and calculate type II and III sums of square, but I have an > empty cells, so anova function from package car fail. (I believe) > > > y<-c(7,13,6,10,8,11,8,3,7,5,65) > > a<-as.factor(c(1,1,2,2,3,3,3,1,1,1,2)) > > b<-as.factor( c(rep(1,7),rep(2,4)) ) > > table(b,a) # cell (2,3) is empty > > mod<-lm(y~ a+b+a:b) > > library(car) > > Anova(mod,type="II") # don't work > > How can I calculate type II and III sum of square whit empty cell? > > Thanks a lot > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
