Exploring the eco-anxiety continuum: calibrating scales with item response theory

Eco-anxiety, defined as the psychological distress related to awareness of climate change, has gained increasing attention but remains conceptually and empirically fragmented. Existing tools such as the Climate Change Anxiety Scale (CCAS) and the Hogg Eco-Anxiety Scale (HEAS) capture only partial aspects of the phenomenon. This study aimed to test the continuum hypothesis of eco-anxiety by jointly calibrating these two instruments within an item response theory (IRT) framework. A French sample of 534 participants completed a combined version of the CCAS and HEAS, analyzed using the Graded Response Model. Results showed a satisfactory unidimensional fit, with all items displaying acceptable discrimination. The HEAS predominantly assessed moderate manifestations, while the CCAS reflected more severe functional impairments. However, nearly a quarter of respondents with the lowest levels of eco-anxiety were not captured by either scale, indicating insufficient coverage of the mildest forms. External validity was supported through strong correlations with negative emotions and emotion-focused coping, but weaker associations with action-oriented strategies. These findings support the eco-anxiety continuum and highlight the need for refined tools capable of covering its entire spectrum, from adaptive concern to clinical manifestations.