Equity in Choosing Wisely and beyond: the effect of health literacy on healthcare decision-making and methods to support conversations about overuse.

Objective: To (a) examine whether the effect of the Choosing Wisely consumer questions on question-asking and shared decision-making (SDM) outcomes differs based on individuals' health literacy and (b) explore the relationship between health literacy, question-asking and other decision-making outcomes in the context of low value care.

Methods: Preplanned analysis of randomised trial data comparing: the Choosing Wisely questions, a SDM video, both interventions or control (no intervention). Randomisation was stratified by participant health literacy ('adequate' vs 'limited'), as assessed by the Newest Vital Sign.

Main outcome measures: Self-efficacy to ask questions and be involved in decision-making, and intention to engage in SDM.

Participants: 1439 Australian adults, recruited online.

Results: The effects of the Choosing Wisely questions and SDM video did not differ based on participants' health literacy for most primary or secondary outcomes (all two-way and three-way interactions p>0.05). Compared with individuals with 'adequate' health literacy, those with 'limited' health literacy had lower knowledge of SDM rights (82.1% vs 89.0%; 95% CI: 3.9% to 9.8%, p<0.001) and less positive attitudes towards SDM (48.3% vs 58.1%; 95% CI: 4.7% to 15.0%, p=0.0002). They were also more likely to indicate they would follow low-value treatment plans without further questioning (7.46/10 vs 6.94/10; 95% CI: 0.33 to 0.72, p<0.001) and generated fewer questions to ask a healthcare provider which aligned with the Choosing Wisely questions (χ² (1)=73.79, p<.001). On average, 67.7% of participants with 'limited' health literacy indicated that they would use video interventions again compared with 55.7% of individuals with 'adequate' health literacy.

Conclusion: Adults with limited health literacy continue to have lower scores on decision-making outcomes in the context of low value care. Ongoing work is needed to develop and test different intervention formats that support people with lower health literacy to engage in question asking and SDM.