Beyond Aggregates

This paper develops a bottom-up, sector-specific approach to modeling potential output that overcomes limitations of traditional top-down estimates for long-term projections and policy analysis. The model disaggregates total-factor productivity (TFP) growth into within-sector productivity effects and between-sector reallocations. Such endogenous between effects capture structural transformation, notably the shift from low-productivity sectors like agriculture to higher-productivity industrial and service sectors-a key driver of growth in developing countries. At the heart of the framework, wedges in sectoral factor prices, substitution elasticities, and productivity differentials describe the contribution of between-effects to aggregate productivity. Although the approach here can be applied to any macro-structural model, its benefits are illustrated by introducing it into the World Bank's semi-structural models for Ghana and the Kyrgyz Republic to showcase its potential to enhance the analysis of long-run growth dynamics through structural change