Notes
Is equal to NextAppointmentDate is available.
If NextAppointmentDate is missing, NextAppointmentDateComputed is equal to:
--- VisitDate + 30 days (one month) if the patient was on ART (onART==1)
--- VisitDate + 183 days (6 months) if the patient was non on ART (onART==0)
cf. section 19 in TasP definitions document for more detail.