https://data.oecd.org/natincome/net-lending-borrowing-by-sector.htm
http://www.transparency.org/news/feature/europe_and_central_asia_an_overall_stagnation
https://www.dbresearch.de/PROD/RPS_DE-PROD/PROD0000000000523908/Deutschland%3A_Konjunktur_kurzgefasst.PDF