[R] Odds ratios for categorical variable

[Roger D. Peng]

Is hab coded as a factor or a numeric variable?

-roger

Sabrina Russo wrote:
> Dear R-users:
> How does one calculate in R  the odds ratios for a CATEGORICAL predictor 
> variable that has 4 levels.  I see r-help inquiries regarding odds ratios 
> for what looked like a continuous predictor variable.  I was wondering how 
> to get the pairwise odds ratios for comparisons of levels of a categorical 
> predictor variable.  I can't seem to get the correct output using:
>  > sp.glm=glm(cohort$logreg~cohort$hab, family=binomial)
>  > summary(sp.glm)
> 
> This gives me the coefficient for the effect of hab overall, but not the 
> coefficients for the comparisons of each of the levels. I suspect this has 
> something to do with the contrasts statement, but I can't figure it out, 
> and would be very appreciative of any help you can provide.
> Thank you,
> Sabrina
> 
> ______________________________________________________________
> Sabrina E. Russo
> Postdoctoral Fellow
> Center for Tropical Forest Science - Arnold Arboretum Asia Program
> Harvard University
> 22 Divinity Avenue
> Cambridge, MA 02138 USA
> 
> 617-496-2380 phone
> 617-495-9484 FAX
> srusso at oeb.harvard.edu
> 
> 
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