I have longitudinal data (4 year follow-up) of brain volume. I now want to investigate whether the change over time of brain volume differs between left and right sides (the idea is that in the disease that I investigate that the right side might show steeper decline in volume over time).
I have reshaped my data in longitudinal format in such a way that time and side are long (so 8 rows per subject). Now I want to run mixed models, but I am wondering whether my model is correct:
model = lme(Brainvol ~ Age + time * side, random=~1|ID, na.action="na.omit", data=long) summary(model)
Would this be correct? Should I add
side as random intercept? I have 150 subjects.
The image shows the organization of the data: SID (subject identifier), times (longitudinal measures, three time points shown), Hipp (volume of a region of the brain), side (left and right).