[R] Error when using polr() in MASS

[Tord Snall]

Dear all,

I get an error message when I use polr() in MASS. These are my data:

   skugg grupp frekv
4      1   gr3     0
5      2   gr3     3
6      3   gr3     6
10     1   gr5     1
11     2   gr5    12
12     3   gr5     1
> 
> summary(polr(skugg ~ grupp, weights=frekv, data= skugg.cpy1.dat))
Error in optim(start, fmin, gmin, method = "BFGS", hessian = Hess, ...) : 
        non-finite value supplied by optim

Does this depend on the very few observations in skugg 1 - the
proportional-odds assumption doesn't hold (p 231, MASS 3ed)? If so, I would
be happy for a recommendation on another approach.

And I also have a similar data set where only the skugg classes 2 and 3 are
observed. Would you recommend glm, family= binomial for that analysis?

I use R 1.6.2, MASS 7.0-10, Win 2000. 


Thanks in advance!

Please reply also to me because I'm on the once a day-list


Sincerely,
Tord

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Tord Snäll
Avd. f växtekologi, Evolutionsbiologiskt centrum, Uppsala universitet
Dept. of Plant Ecology, Evolutionary Biology Centre, Uppsala University
Villavägen 14			
SE-752 36 Uppsala, Sweden
Tel: 018-471 28 82 (int +46 18 471 28 82) (work)
Tel: 018-25 71 33 (int +46 18 25 71 33) (home)
Fax: 018-55 34 19 (int +46 18 55 34 19) (work)
E-mail: Tord.Snall at ebc.uu.se
Check this: http://www.vaxtbio.uu.se/resfold/snall.htm!
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