Gjalt-Jorn,

You might want to check out the Model specification section of
http://glmm.wikidot.com/faq

Between this and the Nieuwenhuis link you probably have everything you
need...

HTH

Alan

--------------------------------------------------
Email: aghaynes@gmail.com
Mobile: +41794385586
Skype: aghaynes


On 5 November 2012 16:03, Gjalt-Jorn Peters <gjalt-jorn@behaviorchange.eu>wrote:

> Dear all,
>
> I posted a question last week, but I haven't received any replies - I'm
> not sure why (because there were no replies :-)), but hereby I try again,
> this time taking it one question at a time.
>
> I don't manage to find a clear explanation of the lmer model specification
> syntax. I haven't been able to find a webpage explaining this. I did find
> some archived posts of this list, and a variety of webpages, but some
> resources seem outdated, and explanations often seem to assume proficiency
> with mixed models and/or prior knowledge of some parts of the
> specification. Which is a bit of an obstacle when you're new to both R and
> lmer :-)
>
> Did I just overlook a resource, or does nothing exist yet and is this
> knowledge indeed kind of fragmented over the internet? I've been struggling
> with this for a few weeks now (not full-time though :-)), but perhaps I'm
> missing crucial search terms or something.
>
> If no source like this exists yet, could somebody perhaps correct my
> inferences? If one or more of you are willing to provide some feedback, I
> can hopefully write a tutorial/webpage thing (similar to, e.g.
> http://www.rensenieuwenhuis.**nl/r-sessions-16-multilevel-**
> model-specification-lme4/<http://www.rensenieuwenhuis.nl/r-sessions-16-multilevel-model-specification-lme4/>,
> but a bit more complete, and similar to Douglas Bates' article at
> http://cran.r-project.org/doc/**Rnews/Rnews_2005-1.pdf<http://cran.r-project.org/doc/Rnews/Rnews_2005-1.pdf>,
> but a bit more geared towards relative lay people). From a variety of
> sources, I pieced together the following.
>
> The basic form is 'criterion ~ formula', where formula specifies the model
> you use to predict the criterion. This model consists of one or more terms
> separated by plusses (+). A term can be:
> -- 1 -> specifies that the intercept should be estimated. Is in fact
> optional as the intercept is always estimated;
> -- a variable name >- specifies that coefficient of that variable should
> be estimated (i.e. its slope);
> -- an interaction term, consisting of two or more variable names separated
> by colons -> specifies that the interactions between all those variables
> should be estimated, as well as their regular coefficients;
> -- a specification of random effects, which can take a number of forms:
> ---- (1 | variable name) -> for each level of variable name, random
> intercepts are estimated
> ---- (variable name 1 | variable name 2) -> for each level of variable
> name 2, random slopes are estimated for variable name 1, and random
> intercepts are estimated (note: '1 + ' implicit, see first bullet);
> ---- (0 + variable name 1 | variable name 2) -> for each level of variable
> name 2, random slopes are estimated for variable name 1, but only one
> (fixed) intercept is estimated;
> ---- (variable name 1 + variable 2 | variable name 3) -> for each level of
> variable name 3, random slopes are estimated for variable name 1 and
> variable name 2, and random intercepts are estimated;
> ---- (variable name 1 | variable name 3 : variable name 2) -> for each
> unique combination of levels of variable name 2 and variable name 3 (where
> variable name 3 is the higher level), random slopes are estimated for
> variable name 1;
> ---- (variable name 1 | variable name 2 / variable name 3) -> for each
> level of variable name 2, which is nested within variable name 3, random
> slopes are estimated for variable name 1;
>
> The next step would be to generate a series of potential scenarios and
> providing syntax for each scenario, like Rense Nieuwenhuis does at
> http://www.rensenieuwenhuis.**nl/r-sessions-16-multilevel-**
> model-specification-lme4/<http://www.rensenieuwenhuis.nl/r-sessions-16-multilevel-model-specification-lme4/>
> .
>
> I hope somebody either knows a resource that roughly does this, or thinks
> it may be nice to help make something like this!
>
> Kind regards, and thank you in advance,
>
> Gjalt-Jorn Peters
>
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