I have (in my opinion) a nested data-set, which I want to analyze with a mixed effects model (R's lme4 function). I need help with the model specification. The data-set consists of three subject groups ('group': control, disease due to gene1, same disease due to gene2) with 15, 10 and 10 subjects respectively. The brain MRI of each subject was subdivided in 78 anatomical regions ('region') and for each region 1 observation of tissue integrity ('value') was made, so 2730 observations in total. The within-subject variability is high, as expected due to the different anatomical locations, whereas the between-subject variability in each region is low. Nevertheless, I am trying to find if there are anatomical regions showing different values between groups. What about this model?
m1 = lmer(value ~ group + region + (1|subj))
Thanks in advance!