Fagerholm, 2016, pp. 16-40. Fagerholm, Andreas (2016). «What is left for the radical left? A comparative examination of the policies of radical left parties in western Europe before and after 1989». Journal of Contemporary European Studies25 (1): 16-40. doi:10.1080/14782804.2016.1148592.
Lachat, 2017, p. 5. Lachat, Romain (2017). «Which way from left to right? On the relation between voters’ issue preferences and left–right orientation in West European democracies». International Political Science Review: 1-17. doi:10.1177/0192512117692644.