🚀 go-pugleaf

In article <1992Oct30.120219.480@hnrc.tufts.edu> jerry@hnrc.tufts.edu 
(Jerry Dallal) writes in reply to me:
>> I was analyzing a large but somewhat sparse contingency
>> table on BMDP 4F.  I noticed, almost by accident, that the program was
>> not calculating the degrees-of-freedom for some log-linear models correctly.
>>                           [ ... ]
>> "We recommend that you add a constant to all cells when you have empty
>> cells in your data that are not to be treated as structural zeros. 
>> Otherwise, some of the analyses ARE NOT PERFORMED CORRECTLY."
>
>Let's be fair.  This is not an easy problem.  The correct number of degrees of
>freedom depends not only on the pattern of structural zeros, but on the model
>being fitted to them.  

I don't dispute that finding degrees of freedom for a complicated model with 
structural zeros is non-trivial.  My point was that in this table I was *not*
assuming any structural zeros.  For a complete table, the df depend *only* on
the model and not on any pattern of *observed* zeros.  BMDP 4F has a
feature for identifying structural zeros which I had not invoked.  If
the program was arbitrarily assuming that observed zeros were
structural, at the very least it should have printed out a message to
that effect.



>>>>>>>>>>>>>>>>>>>bickis@math.usask.ca<<<<<<<<<<<<<<<<<<<<<<<<<<<
Mik Bickis       \,,,       .*#*.  \    University of Saskatchewan
Department of        \,,,  ^\\|//^  ```\   Saskatoon, Saskatchewan
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