[R-lang] Random slopes

[Zhenguang Cai]

Hi all,

I built the following models and did a comparison of them (to determine 
whether I should include in the model the subject slope for the 
interaction).

model1 <- lmer (Y ~ A*B+(A+B+1|Subject)+(1|Item), data=dat, family=binomial)
model1 <- lmer (Y ~ A*B+(A*B+1|Subject)+(1|Item), data=dat, family=binomial)

In order to determine whehter the inclusion of the subject slope for the 
A*B interaction signficantly improves the model fit, I did a comparison 
of the the two models.

anova (model1, model2)

In the output, model1 was autmoatically changed into

model1 <- lmer (Y ~ A*B+(A:B+1|Subject)+(1|Item), data=dat, family=binomial)

What does the A:B mean here? In my original model, I intended to have 
the main effects of A and B (i.e., A+B). Is there any other way to 
determine whether the subject slope for the A*B interaction shold be 
included in the final model?

Thanks,

Zhenguang

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