[25: Eurobarometer Spezial 338 (April 2010), Eurobarometer Spezial 407 (November 2013) und Eurobarometer Spezial 445 (Juni 2016).]
[25: Special Eurobarometer 338 (April 2010), Special Eurobarometer 407 (November 2013) and Special Eurobarometer 445 (June 2016)]