[R] logistic regression with percentages

Peter Dalgaard BSA p.dalgaard at pubhealth.ku.dk
Mon Feb 12 13:16:56 CET 2001

"Oscar" <orp at intras.es> writes:

> Hello
> I've got some data and I want to fit a binomial glm. The problem is that =
> I don't have the number of successes or failures, I have only the =
> percentages. If I want to make all these numbers integers, I have to =
> multiply them for 1000, because there are some low percentages (0.05%). =
> Besides, I don't know if this is correct.
> Any help?
> Thanks in advance, and sorry for my english
> Julio G=F3mez

If you really only have percentages, then your analysis will come out
wrong whatever you do: It makes a substantial difference whether 50%
means "1 of 2" or "316 of 632"!

If you can get the total number in each group, you should *divide* the
percentages by 100 to get probabilities and use the weight= argument
to glm with the number of cases.

   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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