[R] NA in rlm
Rafael A. Irizarry
ririzarr at jhsph.edu
Tue Mar 19 15:49:00 CET 2002
i am using R 1.5 on solaris 2.8 and redhat 7.2 (what i mention
below happens for all of these and on R-1.4.1 on solaris 2.8)
i am fitting an addtive model (y=roweffect+columneffct+error) to the
following data using rlm
8.631371 8.219719
12.407817 12.373610
10.558580 10.284926
11.525872 11.504441
12.644998 12.583985
12.772225 12.629980
12.482169 12.271868
12.039199 12.061671
11.892378 11.688070
11.725565 11.655078
11.251226 11.383293
9.199893 7.860003
12.275562 12.240147
13.638981 13.381291
13.205941 13.060880
11.056920 10.707565
if the above matrix is x, when i do the following:
m <- dim(x)[1]
n <- dim(x)[2]
rows<- as.factor(rep(1:m,n))
cols <- as.factor(rep(1:n,rep(m,n)))
z <-rlm(as.vector(x)~cols+rows,psi=psi.bisquare)
i get an NA in the estimate z$coef[13]
this relates to the 12th row effect which appears to be an
outlier. is this how one interprets an NA here?
one consequence is that i cant get standard errors
through summary.rlm(z). is there a "work around" this?
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