http://www.economics-ejournal.org/economics/journalarticles/2017-10
https://www.imk-boeckler.de/download-proxy-for-faust/download-pdf?url=http%3A%2F%2F217.89.182.78%3A451%2Fabfrage_digi.fau%2Fp_imk_report_159e_2020.pdf%3Fprj%3Dhbs-abfrage%26ab_dm%3D1%26ab_zeig%3D8946%26ab_diginr%3D8482
https://www.dbresearch.de/PROD/RPS_DE-PROD/PROD0000000000523908/Deutschland%3A_Konjunktur_kurzgefasst.PDF
https://library.fes.de/pdf-files/wiso/14700.pdf