PROJECT ABSTRACT The search for effective strategies to prevent or treat Alzheimer's Disease and Alzheimer's Disease Related Dementias (AD/ADRD) is a global public health priority. This search has been exceptionally difficult, reflecting the complex, multi-factorial processes culminating in AD/ADRD, diagnostic ambiguity, and the intrinsic challenges of research on diseases of the brain. Methods in Longitudinal Research on Dementia (MELODEM) is an international initiative to strengthen, harmonize, and promulgate analytic and design approaches for AD/ADRD research. Launched in 2012, MELODEM convenes an international interdisciplinary group of researchers (e.g., epidemiologists, neuropsychologists, neurologists, biostatisticians), across career stages, to identify and address common methodologic challenges in quantitative research on AD/ADRD. These methodologic challenges—such as selection/attrition, reverse causation, and measurement of cognition and dementia—have the potential to bias estimates of the extent to which risk factors protect against AD/ADRD or slow the progression of AD/ADRD. Some biases can be so extreme as to reverse the direction of estimated effects (e.g., protective instead of harmful). For the past decade—the past 4 with support from an R13 award from NIA—MELODEM has convened an annual in-person meeting of 30-40 researchers and twice-monthly web-based meetings on methodologically themed topics. The proposed continuation of our R13 grant will support annual in-person MELODEM meetings to foster development and dissemination of valid and rigorous analytical approaches for quantitative research on the prevention and treatment of ADRD, with the goals of (a) developing new methods when needed, (b) reaching consensus on “best practices” for analytic methods, and (c) providing a platform to share and teach methods to early-career and established researchers. To continue working towards rigorous analytical approaches and “best practices,” the MELODEM annual progress meeting will include both “Data Workshops” and “Discussion Sessions” on topics relevant to current methodological challenges in AD/ADRD research. The grant will also provide travel support for US researchers to participate in the annual meeting and ancillary activities. Finally, to sustain the collaborations and ideas discussed during the meeting, the grant will support post-meeting activities culminating in published reports from the collaborative research stemming from the conference and connections with a broader group of researchers not able to attend the meetings in person. These activities include web-based conference calls and small working group meetings. Support for the proposed MELODEM meetings will strengthen quantitative research methods related to AD/ADRD, foster a collaborative, interdisciplinary community addressing the most important technical challenges, and promote rapid adoption of best practices for solving shared technical challenges in research on preven...