[R-sig-ME] partially crossed design, longitudinal

Thierry Onkelinx thierry@onkelinx @ending from inbo@be
Tue May 29 12:18:27 CEST 2018

Dear Christiano,

IMHO, the easiest solution would be to fit the model with the 5 level time
variable and then calculate the relevant post-hoc contrasts. e.g pert =
(pert early + pert late) / 2

Thinking about the analysis at the design stage of an experiment is

Best regards,

ir. Thierry Onkelinx
Statisticus / Statistician

Vlaamse Overheid / Government of Flanders
Team Biometrie & Kwaliteitszorg / Team Biometrics & Quality Assurance
thierry.onkelinx using inbo.be
Havenlaan 88 bus 73, 1000 Brussel

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


2018-05-25 22:49 GMT+02:00 Cristiano Alessandro <cri.alessandro using gmail.com>:

> Hi all,
> I have a longitudinal study in which I measure the outcome variables at
> baseline condition (bas), then I apply a perturbation (pert) and I measure
> the outcome variable twice (early and late after perturbation is applied),
> and then I remove the perturbation (noPert) and I measure twice (early and
> late after perturbation is applied).
> I would like to use mixed models for this design, but I am a bit confused
> on how to do it. I could just have a single fixed effects 'time' with
> levels 1 to 5, where level 1 would be baseline, level 2 would be pert/early
> and so on. I think this is not the best design though. Alternatively, I
> could use a fixed effects 'condition' with levels bas, pert, noPert,
> crossed with another fixed effect 'time' with levels early/late. However,
> this last design has the problem that I do not have early/late for baseline
> actually.
> Do you have suggestion of what to do in a case like this?
> Thanks a lot
> Cristiano
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