I am collecting longitudinal data using for 4 time waves. Although the survey is administrated to the same population, different individuals may decide to complete it at each time point. As a result there are a number of individuals that only completed it once, others that completed it twice, some that completed it three times and others who participated in all four waves. For example at the moment there are about 2000 participants in time 1 and 1900 for time 2 but only 1200 that participated in both time 1 and time 2 (at the moment i am still collecting data for time 3 so i don't know yet what the final matched sample will be).
The data are from different organizations so I would like to model this with using mixed effects with the lmer in R. e.g.
lmer(outcome~"some repeated variables"+"organization level variables"+timewave+(timewave|subject)+(1|organizations))
My questions are