So I want to use the mixed command. I have 3 different time points. I want to do a regression at time point 3 to see the effect of 'group' on 'score'. I tried to create a variable for score when time=3 (score3). Obviously this has a lot of missing data points as it's only got a number when time=3. Then I tried use the mixed command with score3 as the outcome i.e.
'''
mixed score3 group time || id:, mle
'''
Stata said it couldn't run this because there were too many missing data points in score3.
What do I do?