Problem With Model.Tables Function
I believe that these are correct, but you haven't told us why you think they are wrong. In the unbalanced case you need to understand carefully what to expect: your expected answer is definitely wrong, which suggests that R's might well be right. For the record, these R results agree with S-PLUS on your examples. But they are not much documented in the unbalanced case, so perhaps `for experts only'. The FAQ says: 9.1 What is a bug? .... If a command does the wrong thing, that is a bug. But be sure you know for certain what it ought to have done. If you aren't familiar with the command, or don't know for certain how the command is supposed to work, then it might actually be working right. Rather than jumping to conclusions, show the problem to someone who knows for certain.
On Sat, 10 Mar 2001, Gary Whysong wrote:
[...]
blocks2<-factor(c(1,2,3,4,1,2,4,1,2,3)) trtmts2<-factor(c(1,1,1,1,2,2,2,3,3,3,)) data2<-c(10,12,9,11,13,15,16,18,22,17) unbalanced<-aov(data2~blocks2+trtmts2) summary(unbalanced)
Df Sum Sq Mean Sq F value Pr(>F) blocks2 3 18.267 6.089 7.4341 0.0410993 * trtmts2 2 126.557 63.279 77.2587 0.0006367 *** Residuals 4 3.276 0.819 --- Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1
model.tables(unbalanced,"means")
Tables of means
Grand mean
14.3
blocks2
1 2 3 4
13.67 16.33 13 13.5
rep 3.00 3.00 2 2.0
trtmts2
1 2 3
10.68 14.47 18.97
rep 4.00 3.00 3.00
We find that the treatment means (trtmts2) are incorrect although the
number of replications indicated are correct. Block means (blocks2) are
correct.
The treatment means should be: 10.5, 14.67, and 19.0, respectively.
Why? These are *model*.tables not *data*.tables. You have to adjust for block effects, and they are unbalanced. Blocks 3 and 4 have lower responses than 1 and 2, and they are missing for treatments 2 and 3. Seems to adjust correctly to me. Note the order of terms matters in unbalanced models.
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 272860 (secr) Oxford OX1 3TG, UK Fax: +44 1865 272595 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._