"Fachserie 11, Reihe 1"(PDF) (in German). Statistisches Bundesamt. 5 November 2013. p. 282. Archived from the original(PDF) on 17 November 2014. Retrieved 15 April 2014.
"Fachserie 11, Reihe 1"(PDF) (in German). Statistisches Bundesamt. 5 November 2013. p. 282. Archived from the original(PDF) on 17 November 2014. Retrieved 15 April 2014.