Data Collection

Much of the data collected in the study is recorded during in-person visits at clinical sites but there are telephone visits and remote assessments.

Most importantly, all sites operate a standardized set of procedures that are defined by the protocol for that specific phase of the ADNI study. This allows data collected across participants from the dozens of ADNI sites to be compared cross-sectionally as well as longitudinally.

The data that are collected from these clinical visits can, in broad strokes, be grouped into one or more of the following categories:

  • Subject Characteristics – Demographic information, family history of AD, self-reported medical history and medications, and questionnaires intended to assess non-biological determinants of health..

  • Clinical Assessment - This includes diagnostic information, assessments of cognitive function and daily living, as well as physical and neurological exams.

  • Biofluid Collection - Samples of bodily fluids, including blood, urine, and cerebrospinal fluid (CSF), which are used for analysis of AD biomarkers, as well as genetic information including: Apolipoprotein E (APOE) genotype, genome wide association screening (GWAS), whole genome sequencing, methylation profiles, transcriptomics, RNA sequencing, and omics (e.g. proteomics, lipidomics, metabolomics) profiles.

  • Neuroimaging - Direct measurements of the structure, function, and molecular characteristics of the living brain. This includes functional and structural magnetic resonance imaging (e.g. T1, T2, FLAIR, GRE, DTI, fMRI, and others), positron emission tomography (e.g. FDG PET, amyloid PET and tau PET, with different PET ligands for amyloid and tau), and other imaging modalities.

  • Digital data - In some phases of ADNI, the results of assessments administered in a digital (online) setting were obtained. The instruments include: Cogstate Brief Battery, Novoic Storyteller, Everyday Cognition 12-item questionnaire, and more.

  • Neuropathology – ADNI participants are asked to consider brain donation following death. The Neuropathology Core coordinates the brain donation program and produces tabular data as well as digitized slide images that are available for study.

Note that not all data collection is carried out during in-person clinical visits, particularly in the case of longitudinal follow-up visits, and during the COVID-19 pandemic of 2020-2022. Depending on the procedures scheduled for a given visit, information can also be collected over the phone, via mail-in questionnaires, or digitally.

The recording of information

A key factor to consider when thinking about the ADNI data set is the intermediate step between data collection and the creation of the digital records, as this process has introduced a great deal of variability to the data set.

The exact pathway that information takes between in-clinic collection and public availability varies between different modalities. Images are processed and subjected to rigorous quality assurance procedures, biofluid samples are loaded into vials and shipped out to ADNI labs for analysis and banking, etc.

Of particular note for the tabular ADNI data set is the recording of clinical assessments and questionnaires. These are generally administered to participants by clinicians using pen-and-paper worksheets, which are later transcribed into an electronic data capture (EDC) system by site staff.

There have been multiple iterations of the EDC system used in ADNI, which is sometimes reflected in the format and structure of tables.

Note that the data collected in-clinic are updated on a nightly basis. The date on which a table was downloaded is appended to the filename.

When reporting ADNI data in presentations and publications it is critical to indicate the date of data download (since data updates over time, noting time stamps is key to allowing for reproducibility).