Development of a measure to assess the quality of proxy decisions about research participation on behalf of adults lacking capacity to consent: the Combined Scale for Proxy Informed Consent Decisions (CONCORD scale)

BACKGROUND: Recruitment of adults lacking the capacity to consent to trials requires the involvement of an alternative ‘proxy’ decision-maker, usually a family member. This can be challenging for family members, with some experiencing emotional and decisional burdens. Interventions to support proxy consent decisions in non-emergency settings are being developed. However, the ability to evaluate interventions is limited due to a lack of measures that capture outcomes of known importance, as identified through a core outcome set (COS). METHODS: Using established measure development principles, a four-stage process was used to develop and refine items for a new measure of proxy decision quality: (1) findings from a recent scoping review and consensus study were reviewed to identify items for inclusion in the scale and any existing outcome measures, (2) assessment of content coverage by existing measures and identification of insufficiency, (3) construction of a novel scale, and (4) cognitive testing to explore comprehension of the scale and test its content adequacy through interviews with family members of people with impaired capacity. RESULTS: A range of outcome measures associated with healthcare decision-making and informed consent decisions, such as the Decisional Conflict Scale, were identified in the scoping review. These measures were mapped against the key constructs identified in the COS to assess content coverage. Insufficient coverage of areas such as proxy-specific satisfaction and knowledge sufficiency by existing instruments indicated that a novel measure was needed. An initial version of a combined measure (the CONCORD scale) was drafted and tested during cognitive interviews with eleven family members. The interviews established comprehension, acceptability, feasibility, and content adequacy of the scale. Participants suggested re-phrasing and re-ordering some questions, leading to the creation of a revised version. CONCLUSIONS: The CONCORD scale provides a brief measure to evaluate the quality of decisions made on behalf of an adult who lacks the capacity to consent in non-emergency settings, enabling the evaluation of interventions to improve proxy decision quality. Initial evaluation indicates it has content adequacy and is feasible to use. Further statistical validation work is being undertaken. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13063-022-06787-8.