Biostatistics Core: Summary/Abstract The goal of the Biostatistics Core is to ensure that sound designs and statistical analyses are used to meet the overall goals of ADNI4. The ADNI4 application will extend the follow-up of a large portion of the ADNI3 cohort, deepening our understanding of the long-term processes underlying cognitive aging. Moreover, ADNI4 will recruit and follow a new cohort that is more diverse in pathophysiology, current use of disease-modifying treatment, socio-economic status (SES), and underrepresented populations (URPs, e.g., Black, Latinx.) As ADNI’s experts in biostatistical methods and the data across cores, we will collaborate with other ADNI leaders on design and analyses for each research theme: characterizing change, identifying predictors, improving clinical trial design, and discovery. Our Aims are: 1. To support a dynamic sampling plan that will use a broad registry combined with plasma- based screening to obtain a diverse longitudinal cohort, enriched for biomarker study. 2. To provide guidance and support for interim and final analyses, including the Project. 3. To collaborate with other Cores on statistical methods for harmonization across platforms and ligands. 4. To develop new statistical methodology supporting ADNI4 goals, especially in the area of longitudinal models of multiple biomarker trajectories and as needed to address challenges arising from the ADNI4 sampling plan. 5. To provide intellectual leadership and foster communication among biostatisticians interested in ADNI, including sharing of analysis vignettes through LONI and a public Git repository, and extending our widely used, publicly available ADNIMERGE package.