Plewa, Piotr. “The Effects of Voluntary Return Programmes on Migration Flows in the Context of the 1973/74 and 2008/09 Economic Crises”. Comparative Population Studies 37, no. 1-2 (October 26, 2012). Accessed May 29, 2020. https://www.comparativepopulationstudies.de/index.php/CPoS/article/view/94.