LACKO, Roman et al. Efficiency and Productivity Differences in Healthcare Systems: The Case of the European Union. - Registrovaný: Scopus. In International Journal of Environmental Research and Public Health. - Basel : Published by MDPI. ISSN 1660-4601, 2023, vol. 20, no. 1, pp. 1-14. KEGA 001UVLF-4/2020, VEGA 1/0240/20.