Beyond the numbers: what composite indices reveal – and conceal – about trade-offs and synergies in sustainability transitions

Composite indicators measure complex processes like the sustainability transition across the pillars of the Sustainable Development Goals: Planet, Prosperity, People, Partnership, and Peace. Their popularity stems from their simplicity and comparability, but their proliferation raises concerns about ambiguity, overlap, and limited utility in addressing the systemic nature of sustainability transitions. We show that while diverse composite indices provide multiple perspectives, they often emphasize narrow dimensions, creating measurement gaps and complicating comparisons. These measures also obscure key interactions, such as trade-offs (e.g., economic growth vs. equity), synergies, and independence among dimensions. Using Principal Component Analysis, this paper analyses six composite indices globally and in the EU27, finding that sustainability transitions involve systemic trade-offs and synergies. For instance, in the EU27, economic growth and social inclusion are negatively correlated with environmental sustainability. The authors recommend refining the selection of composite indices, improving systemic analysis, and developing interactionsensitive indicators to capture trade-offs and synergies, ensuring more coherent and effective sustainability monitoring. Lastly, the observed variation in sustainability dynamics between global and regional samples suggests that tailored strategies are necessary