[R-sig-ME] meaning of lmer formula

Fox, John jfox at mcmaster.ca
Thu Sep 7 14:27:22 CEST 2017

Dear Don,

> -----Original Message-----
> From: R-sig-mixed-models [mailto:r-sig-mixed-models-bounces at r-project.org]
> On Behalf Of Don Cohen
> Sent: Thursday, September 7, 2017 12:43 AM
> To: Ben Bolker <bbolker at gmail.com>
> Cc: r-sig-mixed-models at r-project.org
> Subject: Re: [R-sig-ME] meaning of lmer formula
> Is there some documentation I should be reading about this rather than asking
> all these questions?  Other than the code, that is?

Have you read the vignette on lmer() in the package? 

	vignette("lmer", package="lme4")

It also appeared as a paper in the Journal of Statistical Software.

It strikes me that your questions can also be answered by just trying the various formulas that you propose and examining the output.

I hope this helps,

John Fox, Professor Emeritus
McMaster University
Hamilton, Ontario, Canada
Web: socserv.mcmaster.ca/jfox

> 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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