Piras, Gianfranco, and Giuseppe Arbia. “Convergence in Per-Capita GDP across EU-NUTS2 Regions Using Panel Data Models Extended to Spatial”. Statistica 67, no. 2 (January 1, 2007): 157–172. Accessed May 17, 2022. https://rivista-statistica.unibo.it/article/view/3513.