I am looking to build a mixed-effects location-scale model in brms, as implemented by Hedeker and Nordgren 2013 ( https://www.ncbi.nlm.nih.gov/pubmed/23761062 ). The parameterization is as such (taken from https://www.jstatsoft.org/article/view/v059c02 ): [Screen Shot 2020-01-28 at 9.01.43 PM] Basic…

This is possible. See the brms_multilevel vignette for details.

Thanks Paul! I see from the vignette how to model the mean values and the “within-subject” variance (i.e., residual variance), using code such as bf(y ~ X1 + (1 |c| subj), sigma ~ 1 + X1 + (1 |c| subj)) but it doesn’t say how to model the “between-subject” variance (i.e., the group-level intercept…

I am not sure I understand. You can predict sigma by whatever covariate you want as you do with X1 above. What is it that you don’t know how to model then?

The sigma that brms allows to model as you have pointed out is the standard deviation of the residuals. However, as in Hedeker and Nordgren 2013 ( MIXREGLS: A Program for Mixed-Effects Location Scale Analysis - PubMed ), I also wish to model the standard deviation of the group effects: In terms of t…

To my knowledge, brms does not let you do this [yet?]. It’s fairly simple to do via stan itself, however. The Williams/Rast/Zimprich paper does not model the between-group SD afaik. So you can either code it up yourself in Stan, or you might be able to use a package of mine ( https://github.com/step…

Did you ever succeed in modeling the BS variance in Stan or brms? If so, I’d love to hear/see how you did it because I’m working on the same problem.

Hi, unfortunately not. This paper ( https://doi.org/10.1080/00273171.2018.1477577 ) seems to have some code to do it in Stan, but I haven’t yet looked at it closely and modified it for my own use. Let if know if you make any progress on it!

Thank you! It does indeed look like they’ve added a BS variance model. I’ll check it out and let you know if I make any progress!

Hi Madeline! Did you ever happen to get this working? I want to compute ICCs for each subject using brms in stan and I’m a little stuck. Curious to know if you’ve figured this out for the group-level?

Mixed-effects location-scale models in brms

Interfaces brms

mike-lawrence June 25, 2020, 11:17pm 10

See here: Mixed-effect Location Scale Model with BS variance model

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Mixed-effects location-scale models in brms

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