[R] glm binomial with no successes

From: juli pausas <pausas_at_gmail.com>
Date: Wed, 27 Feb 2008 10:49:03 +0100


Dear all,
I have a question on glm, family binomial. I do not see significant differences between the levels of a factor (treatment) if all data for a level is 0; and replacing a 0 for a 1 (in fact reducing the
difference), then I detect the significant difference that I expected. Is there a way to overcome this problem? or this is an expected behaviour ? Here is an example:

s <- c(2,4,4,5,0,0,0,0)
f <- c(31,28,28,28,32,37,34,35)
tr <- gl(2, 4)
sf <- cbind(s,f) # numbers of successes and failures summary(glm(sf ~ tr, family="binomial")) # tr ns

sf[8,1] <- 1
summary(glm(sf ~ tr, family="binomial")) # tr significative **

Thanks for any suggestion

Juli

-- 
http://www.ceam.es/pausas

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