METHODS CORE ABSTRACT Timely support for research design, measurement, statistics, data visualization, and results presentation is essential to ensuring the rigor and reproducibility of D-ARC research and driving scientific innovations. Led by an interdisciplinary team of methodological experts with extensive mentoring and consulting experience, the Methods Core will support a broad range of behavioral research in support of the D-ARC's mission in clinical and translational science. Core Faculty will consult with D-ARC investigators and their collaborators on research methodology across the stages of research, from research planning for a grant, to data collection and analysis, to the presentation and discussion of results. In addition to their need for standard statistical support, investigators are challenged by advances in data collection and statistical models leading to ever more complex data sets and planned analyses; this is especially true for early-stage investigators (ESI). Important recent advances include the management and analysis of dense data resulting from smartphones and wearable devices; adaptive intervention strategies; causal inference for non-randomized interventions; latent variable models capturing and summarizing complex patterns of behavior; nuanced longitudinal models that highlight typical patterns of change as well as variability in patterns of change over time, and the challenges posed by implementing and scaling interventions. Planning such research, as well as analyzing and communicating the results, requires the involvement of expert analytic investigators. The Methods Core Faculty are well equipped to handle these complex types of data, in addition to providing more fundamental statistics support. The aims of the D-ARC Methods Core are to 1) Improve the methodological quality, range, and rigor of behavioral research in mental health and HIV through tailored consultations with D-ARC investigators; 2) Deepen the methodological expertise of D-ARC investigators by offering a quantitatively focused Junior Investigator Group (JIG-Quant) to ESI and funding targeted workshops and visiting scholars on cutting-edge methods; and 3) Stimulate new collaborations among Core Faculty and other experts to propel research on innovative behavioral methods, incentivized by two pilot awards. The Core adds value to the UW research enterprise by contributing to the development of the Next Generation of independent investigators and the creation and application of innovative, rigorous, and reproducible methods. Growing the research workforce and supporting improvements and innovations in methodology will lead to superior science, ultimately exerting a greater impact on the co-occurring mental health and HIV epidemics.