Has 20 Years of EU Membership Fostered Regional Income Convergence in Poland? Empirical Evidence for NUTS1, NUTS2, and NUTS3 Regions

The main objective of this paper is to study regional income convergence in Poland from 1990 to 2024 using a novel approach proposed by Phillips and Sul (2007). We divide the study period into two sub-periods: 1990-2004 and 2005-2024, which allows us to compare income convergence before and after accession to the European Union. Our study uses data at different NUTS levels from NUTS1 to NUTS3. Our results show that the hypothesis of income convergence between all regions of Poland is rejected both at each NUTS level and for the whole period and the sub-periods analysed. Our results indicate the existence of convergence clubs between different regions of Poland. The number of convergence clubs depends on both the NUTS level used and the period analysed. At NUTS1 level we identify 1 to 2 convergence clubs and 3 non-convergent regions. At NUTS2 level there are 2 to 4 convergence clubs and 2 non-convergent regions, while at NUTS3 level there are 3 to 7 convergence clubs and 2 non-convergent regions, depending on the period (sub-period). Our results suggest that the higher the NUTS level, the more convergence clubs. Furthermore, our results indicate that after joining the European Union, the number of identified convergence clubs at each NUTS level is at least twice as high as before joining the European Union.