[R-sig-ME] CLMM: Calculate ICC & Assessing Model Fit
Sidoti, Salvatore A.
@|dot|@23 @end|ng |rom buckeyem@||@o@u@edu
Tue Aug 18 05:32:35 CEST 2020
To begin with, I'm not a fan of cross-posting. However, I posted my question on Stack Exchange more than two weeks ago, but I have yet to receive a sufficient answer:
Here's what I've learned since then (hopefully):
1) ICC of a CLMM:
Computed like this:
(variance of the random effect) / (variance of the random effect + 1) If this is correct, I would love to see a reference/citation for it.
2) 95% Confidence Interval for the ICC from a CLMM Model To my current understanding, a confidence interval for an ICC is only obtainable via simulation. I've conducted simulations with GLMM model objects ('lme4' package) and the bootMer() function. Unfortunately, bootMer() will not accept a CLMM model ('ordinal' package).
3) Model Fit of a CLMM
Assuming that the model converges without incident, the model summary includes a condition number of the Hessian ('cond.H'). This value should be below 10^4 for a "good fit". This is straightforward enough. However, I am not as sure about the value for 'max.grad', which needs to be "well below 1". The question is, to what magnitude should max.grad < 1 for a decent model fit? My reference is linked below (Christensen, 2019), but it does not elaborate further on this point:
3) Effect Size of a CLMM
The random variable's effect is determined by a comparison between the full model to a model with only the fixed effects via the anova() function. I found this information on the 'rcompanion' package website:
The output of this particular anova() will include a value named 'LR.stat', the likelihood ratio statistic. The LR.stat is twice the difference of each log-likelihood (absolute value) of the respective models. Is LR.stat the mixed-model version of an "effect size"? If so, how does one determine if the effect is small, large, in-between, etc?
Salvatore A. Sidoti
The Ohio State University
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