Protocols, Phases, and Schedules
The ADNI study has been running continuously for over 20 years, and the study protocols have changed several times throughout its lifespan to maintain relevance with the surrounding scientific landscape.
Different aspects of the protocols are designed and administered by “Cores” of specialized researchers, which are each responsible for dealing with aspects of the study that are relevant to their specific scientific domains. For more information on ADNI’s scientific team structure and governance, see this page of the ADNI website.
While much of the same core information has been collected continuously since the start of the study - for example: Clinical Dementia Rating (CDR) scores, structural MRI images, and fluid biosamples - the details of these procedures, the scheduling of visits, the manner in which information is transcribed into a digital format, the way in which data are stored and structured, and a number of other parameters have changed quite a bit for the majority of data streams.
Phases
ADNI has been funded and carried out in a series of funding cycles that are internally designated as ‘phases’ of the study.
At the time of this writing these phases are, from earliest to latest: ADNI1, ADNIGO, ADNI2, ADNI3, and ADNI4. The timeframes for each of these phases is shown in the figure below:
Each phase of ADNI requires a new Institutional Review Board (IRB) approved Protocol to be implemented. The protocol for each phase outlines the specific procedures, and the data that are collected on each participant according to their specific visit schedule.
For the purposes of this document, we are primarily concerned with how these changes have been reflected in the data set.
The procedures for recording and storing data often changed along with these phases, leading to some inconsistencies in the structure and format of many ADNI tables.
The full details of each protocol are laid out in the procedures manuals for each phase, which can be found on the IDA under the study files interface, in the Study Info -> Study Protocols & CRFs subsection.
Screening Visits
Prior to enrolling in the study, prospective participants undergo a screening visit. The specific procedures carried out in the screening visit can vary by phase and are spelled out explicitly in the procedures manuals for each phase.
During screening, prospective new participants undergo clinical diagnostic evaluation and MRI (but no PET scans), and – if they are able to enroll in the study and choose to do so - are assigned to a schedule of events based on clinical diagnosis at the time of the screening visit.
Not every participant who is screened is enrolled in the study.
Different phases of the study also feature different sets of general inclusion criteria (e.g., fluency in English or Spanish), and exclusion criteria (e.g., MRI contraindications such as an implanted ferromagnetic pacemaker), which can preclude enrollment. Some participants are also lost to follow-up after their screening visit.
Participants who enroll under a particular phase of ADNI and who then consent enter the next phase (e.g., participants initially enrolled in ADNI2 and then joined ADNI3) are almost always allowed to “pass the screening visit” of the next study phase. These participants who roll over from one phase to the next are referred to as ‘rollovers’ in the context of this document.