Jordi Garcia wrote:
Good morning,
I am using R to try to model the proportion of burned area in
Portugal. The dependent variable is the proportion. The family used is
binomial and the epsilon would be binary.
I am not able to find the package to be used when the proportion (%)
has to be used in glm. Could someone help me?
I am using normal commands of glm.. for example:
glm_5<- glm(formula=p~Precipitation, family=binomial(link=logit),
data=dados)
where p is the proportion of burned area, but this error message
apperars:
Warning message:
non-integer #successes in a binomial glm! in: eval(expr, envir, enclos)
That is why I think I am not using the proper glm package.
Thank you very much in advance.
Jordi
Jordi,
Your statistical model is wrong. The binomial family if four counts data
(counts of successes given n trials), not for proportions. To model
proportions, your family is the Beta family. I've modeled proportion
response variables with function betareg of package betareg. If you want
my example applications I can send you code and data off list.
Reference: Ferrari and Cribari-Neto. 2004. Beta regression for modelling
rates and proportions. Journal of Applied Statistics 31:799-815.
Rubén
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