Shared decision making (SDM) is an imperative to ensure optimal care in rheumatology [1], [2]. Since SDM is not consistently used in practice, various interventions have been developed and evaluated to facilitate SDM, such as patient decision aids, decision coaching and health care provider training [3], [4], [5]. Outcome measures in trials of SDM interventions lack standardization [3], [4], [5] limiting the ability to compare study results. To ensure that research conducted over time can be combined to understand the effectiveness of these interventions, a set of the most relevant outcome domains is needed to inform outcome measure selection for future clinical trials.

The goal of the Outcome Measures in Rheumatology (OMERACT) SDM Working Group (WG) is to gain consensus on a Core Outcome Set for trials of SDM interventions (https://omeract.org/working-groups/sdm/). The OMERACT SDM WG is classified as a ‘bolt-on’ group. ‘Bolt-on groups’ describe the additional domains and instruments that are part of a specific intervention, and which are measured in addition to disease-specific core outcome sets. In a clinical trial of SDM interventions, the trial must measure both the core outcome set specific to the concept of SDM and include the disease-specific core outcome set of the clinical trial's study population. By doing so, we ensure that we measure both intervention-specific and disease-specific outcomes.

In 2021, OMERACT endorsed the Core Domain Set of outcomes for rheumatology trials of SDM interventions [6]. This Core Domain Set includes six outcome domains of the SDM process which should be evaluated in trials evaluating the effectiveness and safety of SDM interventions in rheumatology: 1) Knowledge of options; 2) Alignment of chosen option with values; 3) Confidence in the chosen option; 4) Satisfaction with the decision-making process; 5) Adherence to the chosen option; 6) Potential negative consequences (of the SDM intervention) [6]. Initial definitions were developed for each domain based on previous qualitative work and calls with the OMERACT SDM WG.

Recent guidance from OMERACT includes the development and agreement on the definitions and in-depth descriptions of domains to ensure each domain is thoroughly defined and to help inform the search to find instruments that match the domains for inclusion in the Core Outcome Measurement Set [7]. Thus, our group used consensus-building activities with patient research partners (PRPs) with a rheumatic or musculoskeletal disease, clinicians and researchers to develop detailed descriptions and gain consensus on definitions and detailed descriptions of the domains.