Methodological Evolution and Sectoral Applications of the Difference-In-Differences (DiD) Method in Public Policy Evaluation: A Systematic Review (2003–2026)

This study systematizes the scientific literature on the Difference-in-Differences (DiD) method applied to public policy evaluation, with the aim of identifying its methodological refinements and principal fields of application. A systematic review was conducted following the PRISMA 2020 protocol and the Joanna Briggs Institute criteria. The search covered four academic databases, Scopus, Web of Science, EBSCO, and Taylor & Francis, for the 2003–2026 period, resulting in a final sample of 105 indexed articles. The review identified a clear transition from the standard DiD model toward more sophisticated variants, including staggered, spatial, and synthetic DiD designs, as well as the incorporation of instrumental variables (IV-DiD) to address endogeneity biases. The findings reveal four predominant thematic clusters in which DiD has been most extensively applied: sustainability and ecological transition; social dynamics and human capital; public health management; and infrastructure and digital frontiers. Overall, the evidence suggests that the technical evolution of DiD has substantially improved its capacity to address temporal and spatial heterogeneity, consolidating it as one of the most robust methodological tools for evidence-based governance and state accountability.