Колев, Константин, и Мая Цоклинова. „Level of Digitalization and Gross Domestic Product by Regions: Measurement and Dependencies“. Научни трудове, no. 1 (Май 21, 2025): 279–302. отворен на Юли 22, 2026. https://bjiep.e-dnrs.org/index.php/rp/article/view/5039.