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I am quite new to lmer and quite confused about how to select the random effects part of the model.

The data I am working on is divided into dependent and independent variables. Each variable has two grouping factors. 1). sampling time (sample 1:7) and sampling column (1:24, where 1:3, 4:6 and so are replicates).

I have explored these different possibilities, but I am not sure on which is the correct one to use.

fm1 <- lmer(dependent ~ independent +(1 + independent|Sample)+(1+ independent|Column), data=Data)

fm2 <- lmer(dependent ~ independent +(1|Sample)+(1|Column), data=Data)

fm3 <- lmer(dependent ~ independent + (Sample|Column), data=Data)

fm3 is the model with the lowest AIC and BIC values, but I am not sure that this is the right one to use?

Nick Cox
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Jacob Bruun
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    Hi Jacob and welcome! This post provides some excellent explanations of lmers formulas and their interpretation. What the "right" model is depends greatly on your research question and if it makes sense given your data. – COOLSerdash Jul 08 '13 at 12:46

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