Hello all,
Just new to this forum/ML, which seems great to encourage collaboration
between SPSS users (and between expert-non experts).
For my self, I am starting with linear mixed models and trying to specify
the syntax for the model I have in mind. I'm not sure if I'm syntax is
correct and if it the best for my model. Any help would be appreciated. I am
using SPSS 25 on Windows.
As for the model, I have around 20 animals (in 2 age groups) with measures
of brain activity across 12h periods (12 time-points) for a variable number of days
(between 8 and 31) per animal. I am interested in modelling an interaction
between age and hour (I expect age effect at specific hours but not others).
In my understanding of things, I have two random factors: 1) the days where
the recording took place and 2) the animals which participated. As for my
fixed factor, I see 1) time of the day and 2) age group. Time of the day is
a repeated measures but do not seem random to me as these points are
deliberately fixed.
My retained syntax is below. I am using an autoregressive covariance
structure as I expect high correlation between contiguous data point in the
time domain.
MIXED Variable BY Agegroup Day Hour
/CRITERIA=CIN(95) MXITER(100) MXSTEP(10) SCORING(1)
SINGULAR(0.000000000001) HCONVERGE(0,
ABSOLUTE) LCONVERGE(0, ABSOLUTE) PCONVERGE(0.000001, ABSOLUTE)
/FIXED=Agegroup Hour Agegroup*Hour | SSTYPE(3)
/METHOD=REML
/RANDOM=INTERCEPT Day | SUBJECT(animal) COVTYPE(VC) SOLUTION
/REPEATED=Hour*Day | SUBJECT(animal) COVTYPE(ARH1).
Any thoughts regarding the model (choices of random and fixed factors) and
syntax would be appreciated!
Thank you all !
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