<p>Frontier analysis examining the relationship between SDI and ARHL burden among individuals aged 60 and older.</p>

(A) Temporal progression from 1990 to 2021, with color gradients representing years (dark blue: 1990; light blue: 2021). The black line delineates the efficiency frontier. (B) Cross-sectional analysis for 2021, where each dot represents a country or territory. Countries with the largest effective differences (top 15) are labeled in black (e.g., Eritrea, Ethiopia); low-SDI frontier countries (<0.5) with minimal effective differences are shown in blue (e.g., Niger, Chad); high-SDI countries (>0.85) with relatively large effective differences are highlighted in red (e.g., USA, Japan). Dot colors indicate temporal changes in ARHL burden: red represents decreasing YLDs, blue represents increasing YLDs between 1990 and 2021.