[R-sig-ME] Interaction between random and fixed effects

Thierry Onkelinx th|erry@onke||nx @end|ng |rom |nbo@be
Mon May 31 21:10:13 CEST 2021

Dear Vinicius,

What did you ran the interaction as a fixed effect Year:Local or a
random effect (1|Year:Local)?  How did you code Local: as a unique value
for every Local and Year combinations? Please do share output or a minimal
example so we know exactly what you did. I'm still a novice at mind reading.

Best regards,

ir. Thierry Onkelinx
Statisticus / Statistician

Vlaamse Overheid / Government of Flanders
Team Biometrie & Kwaliteitszorg / Team Biometrics & Quality Assurance
thierry.onkelinx using inbo.be
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what the experiment died of. ~ Sir Ronald Aylmer Fisher
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ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey


Op ma 31 mei 2021 om 20:57 schreef Vinicius Maia <
vinicius.a.maia77 using gmail.com>:

> Hi all,
> I have a subtle doubt in how to interpret the interaction between fixed (or
> even random) and random effects in the following case.
> I have a model: Y ~ Year + (1|Local)+(1|Genotype) + (Year:Local:Genotype)
> Year is a fixed effect because it has only 4 levels.
> I ran the model with the random and fixed effect interaction just to
> explore, but I was not expecting that it would work because Locals are
> completely nested within Years.
> To my surprise, the model ran and the variance of Year:Local:Genotype are
> quite big. How is it possible to have Local interacting with Year if they
> are nested? I also tried: Y ~ Year + (1|Local)+(1|Genotype) + (Year:Local)
> and the model rans too, without singular fit.
> I am struggling to understand if random interactions (it also extends to
> cases where the interactions are only between nested random effects) mean
> that the variance between Locals changes with Years or if the effect of a
> given Local changes with Years. If it is the former option I can understand
> why the model ran and has a high variance for the interaction, but if it is
> the later case (which I believe it is), how does the model estimate an
> interaction for Local:Year if they are nested?
> Thanks!
> Best wishes,
> Vinícius Maia
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