[R] NA in rlm

[Rafael A. Irizarry]

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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