@book { VernderungenderZahlungsbereitschaft,
    title = "Veränderungen der Zahlungsbereitschaft",
    author = "Frank {Gärtner}",
    year = "2002",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832456818",
    url = "https://m.diplom.de/document/221159"
}