[R-sig-ME] [Lme4-authors] Fixing the level 1 residual variance

[Ben Bolker]

On 14-05-02 03:43 PM, Douglas Bates wrote:
> On Fri, May 2, 2014 at 9:23 AM, Charlotte Arndt <arndtch at uni-landau.de
> <mailto:arndtch at uni-landau.de>> wrote:
> 
>     Dear Sir / Madam,
>     I am analyzing some data by means of multivariate multilevel models
>     and want to fix the residual variance on level 1 to zero. In HLM,
>     you can do this by fixing the level 1 residual variance (sigma
>     square) to a very small value, e.g. 0.00001. Is it possible to
>     constrain the level 1 residual variance with lme4? It would be
>     great, if I could use lme4 for my analyses. Thanking you in advance.
> 
> 
> I forget how the "levels" are numbered in the multilevel modeling
> literature but as you say "residual variance" I imagine you are
> referring to the variance of the conditional distribution of the
> response given the random effects.  The way the model is defined and fit
> in the lme4 package the covariance matrix of the random effects is
> defined relative to this variance.  In other words it would not be
> possible to fit the model in the way you describe.
> 
> Actually I can't imagine how such a model could make sense.  Where does
> the variability in the conditional distribution get absorbed?


  Actually, this can be done with blme.   See

http://thread.gmane.org/gmane.comp.lang.r.lme4.devel/11500/
http://thread.gmane.org/gmane.comp.lang.r.lme4.devel/11093/