Tvrdoň, Michal, and Karel Skokan. “Regional Disparities and the Ways of Their Measurement: The Case of the Visegrad Four Countries / Regioniniai Skirtumai Ir Jų Matavimo Būdai: Keturių Vyšegrado šalių Atvejis”. Technological and Economic Development of Economy 17, no. 3 (October 4, 2011): 501-518. Accessed August 24, 2019. https://journals.vgtu.lt/index.php/TEDE/article/view/5341.