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

[David Winsemius]

On Oct 21, 2013, at 10:44 AM, Greg Snow wrote:

> If X1 and X2 are both numeric variables then
> 
> Outcome ~ I( X1 + X2 ) + (1|Subject)

Would that be:

Outcome ~ I( (X1 + X2)/2 ) + (1|Subject)  # ?

-- 
David.


> 
> should give you what you need.
> 
> If both are categorical, then you need to create a set of variables
> that represent the combination (make sure that you understand what
> that combination represents).
> 
> On Sun, Oct 20, 2013 at 7:52 PM, Jean-Philippe Laurenceau
> <jlaurenceau at psych.udel.edu> wrote:
>> Dear R-sig-ME list--
>> 
>> When specifying the following lmer model, I get intercept fixed and random effects, a fixed effect for the X1 predictor, and a fixed effect for the X2 predictor.
>> 
>> 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?
>> 
>> Thanks for your time, J-P
>> 
>> Jean-Philippe Laurenceau, Ph.D.
>> Department of Psychology
>> University of Delaware
>> 
>>        [[alternative HTML version deleted]]
>> 
>> _______________________________________________
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> 
> 
> 
> -- 
> Gregory (Greg) L. Snow Ph.D.
> 538280 at gmail.com
> 
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David Winsemius
Alameda, CA, USA