Hi everyone,

I am using a mixed effect model and I would like to provide profile confidence intervals, which were suggested in the lme4 documentation as an alternative to traditional pvalues. Below are my model and the command I use to generate the confidence intervals:

m <- lmer(residRT ~ Gram*Number + (0+Gram+Number|Subject) + (1|Subject)  + (1|Item), data= data, ])  #model
confint(m, method="profile", oldNames=FALSE)  #profile CIs

However, when I run confint () I always get this warning: "In cov2cor(m) : diag(.) had 0 or NA entries; non-finite result is doubtful" (I get it 13 times, one for each parameter in the model). 

My questions are:

(1) How worried should I be? Would you advice not to report the CIs given the warning? When I compute normal CIs intead (same command, just method="Wald) I get values that very similar to the profile confidence intervals. I wonder if I should report normal CIs instead: the upshot is that they can be always computed, but I worry they  are less related to the way the mixed-effects model was computed, so it might be conceptually confusing.

(2) If I were to report the profile CIs, which are the standard references I should give in the paper? I don't think profile CIs are known in my field, so I think I should point people to whichever are the standard references for this.

Thanks for your help!

--Sol




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