[R-sig-ME] meaning of lmer formula

[Jake Westfall]

Hi Don,

Is there some documentation I should be reading about this rather
> than asking all these questions?  Other than the code, that is?


Not sure if it would answer *all* your questions but have a look at the R
GLMM FAQ, the relevant section of which is here:
http://bbolker.github.io/mixedmodels-misc/glmmFAQ.html#model-specification

It's a great resource on mixed models generally.

Jake

On Wed, Sep 6, 2017 at 11:43 PM, Don Cohen <don-r-help at isis.cs3-inc.com>
wrote:

>
> Is there some documentation I should be reading about this rather
> than asking all these questions?  Other than the code, that is?
>
> Ben Bolker writes:
>  >  Separate terms in lme4 formulas are always independent.
>
> In a formula like "out ~ in + ((a | group) + (b | group))"
> do (a | group) and (b | group) qualify as separate terms?
>
>  > (input1|group) + (input2|group) is problematic because both terms
>  > include an intercept.
>
> I was imagining that this duplication was removed after the formula
> was expanded into some internal form (that I'd like to see).  I guess
> you're saying that's not true.
>
>  > (0+input2|group) can be helpful, but doesn't do
>  > what you think when the variable on the LHS (e.g. input2) is a factor.
>
> Where can I read about what that means?
>
>  > If input1 and input2 are both numeric (or 2-level factors) then they're
>  > two independent 3x3s.
>
> I have trouble seeing how factors make sense on the LHS.
>
> Another question:
> I tried an example with about a dozen inputs inside one group
> (in1 + in2 + ... | group1) and another with the same inputs for
> a second group, and both took about a minute, and then when I
> used both groups the run time went up to about 10 min.
> Is this expected and easily explained?
>
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