Public Preferences for Index Aggregation Imply Lower Ocean Sustainability

Sustainability indices are essential to track development progress and guide policy. They often aggregate diverse dimensions into a composite index, requiring value-based choices about the importance of each dimension (weighting) and the extent to which weaknesses in some area can be offset by strengths in others (substitutability). Such choices strongly shape indices but lack empirical support. We introduce a preference-elicitation experiment to align aggregation choices with stakeholder views and apply it to the Ocean Health Index (OHI). Respondents from twelve coastal countries predominantly view OHI goals as complementary, challenging current assumptions of perfect substitutability. Incorporating these public preferences yields substantially lower OHI scores, suggesting that ocean sustainability may be overstated and that policy should focus more on improving the weakest-performing dimensions.