We assume dominant side of disease is not a fixed variable
If at Baseline a subject’s dominant side of disease is ‘Left’ and domside is not recorded for (i.e.) Visit Month 6, this visit and any visit that does not have dominant side info is filled in with ‘Symmetric’ variable
In my opinion: if dominant side ever noted, other missing data should be populated to match (i..e if Left at visit 1, NA on future visits, dominant side remains L) - not symmetric.
https://github.com/alex-reardon/PPMI_merge_Readme/blob/b163bf4060ad474f3a9dff35fc4ce262fda55714/ppmi_merge.Rmd#L810