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2006 May 05
1
trouble with step() and stepAIC() selecting the best model
...plant species using a negative binomial glm. Sometimes, summary(step(model)) or summary(stepAIC(model) does not select the best model (lowest AIC) but just stops before. For some species, step() works and stepAIC don't and in others, it's the opposite. The model is model=glm.nb(sdg.cens1 ~ seed.cens1 + log(in.lit+1) + log(trans.dir+1)+ log(trans.dif+1) + slope +log(pH+1) + log(CN+1) + site, data=data) For example, for species A using stepAIC() I get: Call: glm.nb(formula = tot.rec ~ slope + log(pH + 1) + log(CN + 1), data = data, init.theta = 0.0575099635396228, l...