@book { ASocioEconomicAnalysisofAttendanceBehaviourinCommercialFitnessClubs,
    title = "A Socio-Economic Analysis of Attendance Behaviour in Commercial Fitness Clubs",
    author = "Maren {Mueller}",
    year = "2012",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783656239529",
    url = "https://www.hausarbeiten.de/document/197829"
}