Polcyn, J. and Gawrysiak, M. 2017. Education Index and Level of Social Development as a Background for Examination Results on the Lower and Upper Level of Secondary School. Przegląd Badań Edukacyjnych (Educational Studies Review). 2, 23 (Feb. 2017), 25–44. DOI:https://doi.org/10.12775/PBE.2016.071.