Project Summary Large observational data such as electronic health records (EHRs) and medical claims have become an enabling source for facilitating clinical and translational research including Alzheimer's Disease and Alzheimer's Disease Related Dementia (AD/ADRD). One major challenge for conducting observational AD/ADRD studies is about phenotyping – there is a lack of a centralized repository for hosting and standardizing phenotype definitions in AD/ADRD research and few methods have been developed to address bias associated with phenotyping errors in observation data. Therefore, the overarching goal of this proposal is to fully develop a joint effort between medical informaticians, statisticians, clinicians, and epidemiologists with a focus on building a rigorous set of methods and tools for managing phenotype definitions and for correcting bias in observational data analysis, through modern knowledge engineering and data-driven statistical modeling. To achieve that goal, we propose three specific aims in this study: (1) Aim 1 - Collect, normalize, and share definitions of common phenotypes used in AD/ADRD observational research; (2) Aim 2 - Develop novel algorithms to correct bias associated with phenotyping errors when users apply existing phenotype definitions to local data; and (3) Aim 3 - Validate, refine, and disseminate proposed methods and tools by demonstration studies and community engagement. We believe informatics methods and tools proposed here will improve current practice on phenotypic data management and analysis, thus enhancing the reproducibility and quality of observational studies on AD/ADRD.