M. Bickert. The University of Mississippi, Croft Institute for International Studies, University, Bachelorarbeit, (2019)http://thesis.honors.olemiss.edu/1519/7/Bickert%20Thesis.pdf. (GLES).
A. Keute. Norwegian University of Science and Technology, Fac. of Humanities, Master thesis, (2016)http://hdl.handle.net/11250/2414963. (Eurobarometer).