Abstract As health care has become more complex, shared decision making (SDM) becomes increasingly important and is now required by the Centers for Medicare and Medicaid Services (CMS) prior to reimbursement for some services. Despite such requirements, we do not yet have a way to monitor the quality of medical decision-making in today’s practice environment. This void limits the impact of policies requiring the use of SDM as well as the ability to either foster SDM or understand its effects in practice. In this application, we build on our team’s clinical and medical decision-making expertise to develop valid and psychometrically sound, patient-reported SDM-support (SDM-S) measures that consider four distinct, decision-making phases (i.e., choice awareness, consideration of alternatives/preferences, choice-making, and choice implementation), and the language used by patients to describe how decision making unfolds in practice. In so doing, we seek to advance the SDM measurement field from a researcher, single scale orientation to a multiphase/multi subscale orientation that explicitly considers the decision-making support patients describe receiving from their physician and different care team members across each of the decision-making phases from decision awareness to choice implementation. Such an orientation is needed as providers and others explore new and innovative ways to implement and monitor SDM in practice. We use mixed-method and user-centered design approaches to develop the measures and test their performance across four preference-sensitive cancer care contexts: lung cancer screening, colorectal cancer screening, rectal cancer treatment, and prostate cancer treatment. We evaluate scale performance and acceptability among the diverse populations served in real-world primary and oncology care settings. Our specific aims are to: Aim 1. Develop psychometrically sound clinician-specific and overall team SDM-S subscales for each decision phase; Aim 2. Evaluate and compare the predictive validity of the clinician-specific vs. overall team SDM-S subscales across and within decision phases; and Aim 3. Evaluate patient acceptability of SDM-S scales in real-world primary and oncology care settings. Results will enable monitoring the phase-specific quality of SDM-S provided within today’s team-based care models across diverse cancer screening/treatment decisions and patient subgroups. As such, study findings will provide actionable targets for those wanting to monitor and improve patient-centered care and important measurement tools for those studying the impact of SDM on patient and other outcomes. 1