From bolker at ufl.edu  Wed Mar 29 01:51:58 2006
From: bolker at ufl.edu (Ben Bolker)
Date: Tue, 28 Mar 2006 23:51:58 +0000 (UTC)
Subject: [Rd] weights in glm (PR#8720)
References: <20060328173932.D6B581953A@slim.kubism.ku.dk>
	<x2hd5ixuqc.fsf@turmalin.kubism.ku.dk>
Message-ID: <loom.20060329T014422-58@post.gmane.org>

Peter Dalgaard <p.dalgaard <at> biostat.ku.dk> writes:

> 
> I'm not even sure we want to fix this up. I recall some nasty issues
> with DF that have no proper solution that way - an observation with a
> tiny weight represents an observation with a large variance and
> contributes 1DF to the residual, with weight zero it is not supposed
> to contribute at all, so there's a discontinuity for weights
> approaching zero.
> 

  with respect: is it worth adding a note to the documentation
and/or a warning to the code?  I understand that it
becomes unwieldy to warn/protect against all
"stupid"/unforeseen/suboptimal uses of the software, but I also 
understand how the original poster could have decided that setting
a weight to zero was a plausible way to ignore cases ... there is 
already a warning that "observations with zero weight not used for
calculating dispersion" -- could one modify this
slightly to warn people against using zero weights?  (Are zero
weights always a bad idea?)

   Ben Bolker



[Rd] weights in glm (PR#8720)
Ben Bolker