[R-sig-ME] equality constraints in lmer/lme4

[David Duffy]

On Mon, 21 Oct 2013, Jean-Philippe Laurenceau wrote:

> fm <- lmer ( Outcome ~ X1 + X2 + ( 1 | Subject ), data = mydata)
>
> My question: is there a way to ask lme4 to re-estimate this model but 
> set an equality constraint on the effects of X1 and X2, such that their 
> estimates would be equal to each other?

Create the appropriate composite dummy variable (lmer doesn't offer LISREL 
style constraints). For instance, if X1, X2 are categorical then X1=A 
X2=A -> dummy.A=2, dummy.B=0...

Cheers, David Duffy.