[R-sig-ME] Advice for modelling a crossover RCT

[Jorge Teixeira]

Thank you, Chris.

By period I mean the order of the exercise condition within each sequence
(aka cycle).

Maybe cycle/ period resonates better for you. See fig 1 of Individual
responses to topical ibuprofen gel or capsaicin cream for painful knee
osteoarthritis: a series of n-of-1 trials - PubMed
<https://pubmed.ncbi.nlm.nih.gov/33197270/>
https://pubmed.ncbi.nlm.nih.gov/33197270/  .

Carryover effects are irrelevant for the study, imo

A quarta, 12/02/2025, 22:26, Chris Howden <chris using trickysolutions.com.au>
escreveu:

> Hi Jorge,
>
> I'm not sure you are going to have enough sample to fit complex mixed
> models, so I would build them up from a simple one and see how they go. The
> more complex ones may have a hard time converging.
>
> Looks to me like M1 -> Y ~ GROUP + CONDITION + (1 | ID/Sequence) might fit
> and make sense. I would interpret yr notation to mean that each person is
> getting their own random intercept, and then each person's sequence is also
> getting their own random intercept (after accounting for the persons random
> intercept), is that what you are aiming for? If the exercises aren't
> particularly onerous or difficult than I would suspect Sequence will come
> back explaining very little variance and could be dropped - but if onerous
> you might find they do the 2nd one worse, and if difficult the 2nd one
> better as they have time to learn.
>
> But what is PERIOD? (I may be missing something, but I can't see where you
> explain that?)
>
>
> Chris Howden B.Sc. (Hons)
> Founding Partner
> Data Analysis, Modelling and Training
> Evidence Based Strategy/Policy Development, IP Commercialisation and
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> (mobile) +61 (0) 410 689 945 | (skype) chris using trickysolutions.com.au
>
> -----Original Message-----
> From: R-sig-mixed-models <r-sig-mixed-models-bounces using r-project.org> On
> Behalf Of Jorge Teixeira
> Sent: Thursday, 13 February 2025 2:00 AM
> To: R-mixed models mailing list <r-sig-mixed-models using r-project.org>
> Subject: [R-sig-ME] Advice for modelling a crossover RCT
>
> Dear everyone,
>
> I am going to conduct a randomized crossover study where participants
> (about 20) are divided into 2 groups due to logistics constraints. The
> study involves participants performing 4 different exercise modalities
> (i.e., 4 conditions) in a randomized order, in two SEQUENCEs. So, there are
> a total of 8 sessions (2 for each exercise modality), per participant.
>
>
>
> Given this setup, I am unsure about what is the correct mixed-effects
> model to use in this case, and also any further insights or considerations
> you believe I should need... I'll be more than happy to listen!
>
>
>
> Some suggestions:
>
> M1 -> Y ~ GROUP + CONDITION + (1 | ID)
>
> M2 -> Y ~ GROUP + CONDITION + SEQUENCE + PERIOD +  (1 | ID / SEQUENCE /
> PERIOD)
>
>  M3 -> Y ~ GROUP + CONDITION + (1 | ID / SEQUENCE / PERIOD)
>
>
>
> Thank you in advance for the help
>
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