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

[Chris Howden]

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
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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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