1. Ensor T: Informal payments for health care in transition economies. Health Policy. 2004, 58 (2): 237-246.
2. Gaál P, Belli PC, McKee M, Szócska M: Informal payments for health care: definitions, distinctions, and dilemmas. J Health Polit Policy Law. 2006, 1 (2): 251-293.
3. Lewis M: Informal health payments in Central and Eastern Europe and the former Soviet Union: issues, trends and policy implications. Funding Health Care, European Observatory on Health Care Systems Series. Edited by: Mossialos E, Dixon A, Figueras J, Kutzin J. 2002, Buckingham: Open University Press, 184-205.
4. Balabanova D, McKee M: Understanding informal payments for health care: the example of Bulgaria. Health Policy. 2002, 62: 243-273. 10.1016/S0168-8510(02)00035-0.
5. Mastilica M, Bozikov J: Out-of-pocket payments for health care in Croatia: implications for equity. Croat Med J. 1999, 40 (2): 152-159.