[R-sig-ME] Repeated Measures Design With lme Function

Telli Davoodi telli at bu.edu
Mon Feb 12 18:53:17 CET 2018


Dear Thierry,

Thank you for the reply. Just to make sure, after I did a little more
research on my design, I concluded that in my design, Question and Category
are crossed (maybe you have already figured this our from my original
explanation). So, with this in mind, does the syntax you suggest still make
sense with the lme function? Or do I have to run my model with lmer?

Thanks again,
Telli

On Mon, Feb 12, 2018 at 11:18 AM, Thierry Onkelinx <thierry.onkelinx at inbo.be
> wrote:

> Dear Telli,
>
> When you nest question in category, you assume that you have 25 (= 5 x
> 5) different question which are grouped into 5 categories.
>
> In lme4 notation the random effects (1|SubjectID/Category/Question)
> translate more verbose into (1|SubjectID) + (1|SubjectID:Category) +
> (1|SubjectID:Category:Question). This make it more clear that you have
> 3 random intercepts: one per SubjectID, one per combination of
> SubjectID and Category and one per combination of SubjectID, Category
> and Question. That last random intercept has only one observation per
> level and thus doesn't make sense. So I'd go for lme(Essen ~
> AgeinYears * Category * Question, random = ~1|SubjectID/Category) Note
> that I've rearraged the order of the fixed effects. This is yield a
> different parametrisation which seems a bit more appropriate for this
> case.
>
> Best regards,
>
> ir. Thierry Onkelinx
> Statisticus / Statistician
>
> Vlaamse Overheid / Government of Flanders
> INSTITUUT VOOR NATUUR- EN BOSONDERZOEK / RESEARCH INSTITUTE FOR NATURE
> AND FOREST
> Team Biometrie & Kwaliteitszorg / Team Biometrics & Quality Assurance
> thierry.onkelinx at inbo.be
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>
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> able to say what the experiment died of. ~ Sir Ronald Aylmer Fisher
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>
>
>
>
> 2018-02-10 21:59 GMT+01:00 Telli Davoodi <telli at bu.edu>:
> > Hi all,
> >
> > I'm having a hard time defining a model with my repeated measures design
> > (explained below). This is an experimental design and it is fully
> balanced.
> > I would really appreciate it if you have any feedback.
> >
> > Thanks,
> > Telli
> >
> > Here's the design of my experiment: I have 72 children (Subject ID)
> answer
> > five questions (Question) about five different categories (Category).
> > Basically, the same five questions repeat for each category. So, in long
> > format, every participant has 25 rows (five for each level of category
> and
> > within each level of category, question has five levels).
> >
> > Now, I want to fit a mixed-effects regression model on this data, using
> the
> > lme function from the nmle package, but I'm not sure how to account for
> the
> > fact that Category repeats with Subject ID and Question repeats with
> > Category. This is what I have so far, but I'm not sure if I'm specifying
> > the random part of the model correctly:
> >
> > summary(Qs <- lme(Essen ~ Question * AgeinYears * Category,
> > random = ~1|SubjectID/Category/Question, data = Q, na.action = na.omit))
> >
> > I just want to make sure that I am allowing Category to vary within
> > SubjectID and Question to vary within Category.
> >
> > Also, is it correct to say that Category is "nested" under Subject ID and
> > Question is nested under Category?
> >
> >         [[alternative HTML version deleted]]
> >
> > _______________________________________________
> > R-sig-mixed-models at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-sig-mixed-models
>

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