Chris Beeley
2012-Apr-05 08:00 UTC
[R] Extract fitted values with and without offset from glm
Hello- In the notes for the lm function it states " Offsets specified by offset will not be included in predictions by predict.lm, whereas those specified by an offset term in the formula will be." I would like to extract fitted values in just this way from a glm model, those with the offset and those without. I have tried doing things like this: predict.glm(glm(Incident~Numbers, offset=logit(Numbers), family=binomial, data=violdata)) predict.glm(glm(Incident~Numbers+offset(logit(Numbers)), family=binomial, data=violdata)) As well as like this: glm(Incident~Numbers, offset=logit(Numbers), family=binomial, data=violdata)$fitted.values glm(Incident~Numbers+offset(logit(Numbers)), family=binomial, data=violdata)$fitted.values But they return the same result. The first 50 lines of my data look like this: structure(list(Incident = c(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1), Numbers = c(13L, 13L, 13L, 13L, 13L, 13L, 13L, 13L, 13L, 14L, 14L, 14L, 14L, 14L, 14L, 14L, 14L, 14L, 13L, 13L, 13L, 13L, 14L, 14L, 14L, 14L, 14L, 14L, 14L, 13L, 13L, 13L, 13L, 13L, 13L, 14L, 14L, 14L, 14L, 14L, 13L, 13L, 13L, 13L, 13L, 13L, 13L, 13L, 13L, 13L)), .Names = c("Incident", "Numbers"), row.names = c(NA, 50L), class = "data.frame") Any assistance gratefully recieved. Many thanks, Chris Beeley, Institute of Mental Health, UK