Recent research shows that localised economic decline drives important political outcomes, in particular support for populism. Economic decline is measured using long-term administrative data to generate average treatment effects. In this paper, we ask: who can judge economic decline? Using new survey-based measures of localised economics together with a range of contextual data, we reveal the individual-level determinants of economic decline perceptions and the degree to which accuracy is determined by geographic units and types of economic measurement. Using these insights, we reveal the heterogeneous effects of economic decline perceptions on support for Britain’s exit from the European Union (Brexit). The implications of this paper are important for the conclusions we draw about the electoral importance of localised economic decline and inequalities, and the limitations and important scope conditions of those effects.