Schedules and rollovers
Understanding how data collection is scheduled is essential to understanding the longitudinal structure of the resulting data set.
Near the start of every ADNI procedures manual, there is a list of the clinical schedules of events. These are the master lists of procedures and follow-up visits to be carried out during that phase of the study. One such schedule can be seen here:
The column on the far left contains a list of procedures, while each subsequent column is titled with a visit window - screening, baseline, and follow-ups arranged for a particular number of months (e.g., M6 = month 6 follow-up). The check marks indicate whether the procedure specified in each row is to be done during that visit.
This example schedule applies to new AD participants and is specific to the ADNI2 phase of the study. There are separate schedules for participants originally enrolled in a previous phase and chose to continue with longitudinal follow-ups. This is an important procedural distinction and definition used in the ADNI data set:
New participants are newly enrolled in the study during the phase in question.
Rollover participants are participants whose first ADNI visit occurred during a previous phase of the study, under a different protocol.
In general, schedules can vary in two ways: between new participants and rollovers, and between diagnostic groups (CN, MCI, AD/DEM).
In addition, ADNI4 schedules for rollover participants vary based on the timing of a participant’s most recent PET scan, which had occurred under the ADNI3 protocol, in order to limit radiation exposure.
Study partners (informants) in ADNI
The ADNI protocols have included a number of informant-report clinical instruments including the clinical dementia rating (CDR), neuropsychiatric inventory (NPI), and assessment of everyday cognition (ECOG). Because of this, ADNI participants are required to have an informant, or ‘study partner’, to complete these assessments.