Repeated Measures Design With lme Function

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
Havenlaan 88 bus 73, 1000 Brussel
www.inbo.be


///////////////////////////////////////////////////////////////////////////////////////////
To call in the statistician after the experiment is done may be no
more than asking him to perform a post-mortem examination: he may be
able to say what the experiment died of. ~ Sir Ronald Aylmer Fisher
The plural of anecdote is not data. ~ Roger Brinner
The combination of some data and an aching desire for an answer does
not ensure that a reasonable answer can be extracted from a given body
of data. ~ John Tukey

///////////////////////////////////////////////////////////////////////////////////////////




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]]