[R] inconsistent behaviour of add1 and drop1 with a weighted linear model

2007-03-13 Thread Jenny Hodgson 
 the answers I want, 
therefore to explore my model with these functions and avoid using 
add1/addterm?

HUGE thanks for reading to the end! I would be extremely grateful if 
someone could help me with this problem. I wasn't able to find any clues 
in the docs or the r-help archives (but perhaps as it's a complex 
problem I wasn't using the right search terms, if so, apologies)

Best wishes
Jenny

_
Jenny Hodgson
Department of Biology - area 18
PO box 373
University of York
YO10 5YW
UK
Tel: 01904 328623

__
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Re: [R] inconsistent behaviour of add1 and drop1 with a weighted linear model

2007-03-13 Thread Jenny Hodgson 
I was using Version 2.3.1 for Windows (binary download version). Guess I
should be using the latest version, (but the reason is I'm writing up my
PhD and I thought my results would be more 'repeatable' if I didn't keep
changing my version of the software, I didn't really think there would
be any glitches as big as this). Sorry if this is a waste of your time.
And thanks very much for replying so quickly.

Jenny

_
Jenny Hodgson
Department of Biology - area 18
PO box 373
University of York
YO10 5YW
UK
Tel: 01904 328623



Peter Dalgaard wrote:

 Jenny Hodgson wrote:

 Dear R Help,
 I have noticed some inconsistent behaviour of add1 and drop1 with a 
 weighted linear model, which affects the interpretation of the results.
 I have these data to fit with a linear model, I want to weight them 
 by the relative size of the geographical areas they represent.
 _
  

   example
yx1   x2   weights
 1  -4.546477 0.1859556 50.0 0.9466022
 2   1.484246 0.4740497 29.88000 1.3252430
 3   2.203681 0.8594264 16.9 0.9466022
 4   1.943163 0.8713360 42.11765 2.7766997
 5   1.886473 0.9006082 19.0 0.9466022
 6   1.795393 0.8455183 23.68421 1.1674760
 7   1.878077 0.5641396 35.0 0.8203885
 8  -4.215484 0.4356858 58.75000 0.4417477
 9   1.993339 0.5440061 19.28571 0.8519420
 10  1.560869 0.6285066 19.54545 0.8203885
 11  2.761535 0.7017720 15.8 0.1262136
 12  0.995959 0.4638751  0.0 0.9466022
 13 -4.516514 0.2794199 77.85714 0.8834954
   sum(example$weights)
 [1] 13.0

   model-lm(y~1,data=example,weights=weights)
   add1(model,.~.+x1+x2)
 Single term additions

 Model:
 y ~ 1
Df Sum of SqRSSAIC
 none  94.000 27.719
 x1  155.290 38.710 18.185
 x2  158.630 35.371 17.012
   

 Which version of R??!

 I get (2.4.1 on Fedora 6):

  add1(model,.~.+x1+x2)
 Single term additions

 Model:
 y ~ 1
   Df Sum of SqRSSAIC
 none  74.541 24.703
 x1  144.377 30.164 14.942
 x2  136.619 37.922 17.918


__
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.