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).
Brainvol
for both hemispheres in each subject? If so we should add this in your random term. However this depends on how your data is structured. Would you be able to add a snippet of your data table? $\endgroup$ – Stefan Jan 19 '17 at 6:03