@incollection{ZerresLitterst,
  author    = {Zerres, Christopher and Litterst, Florian},
  title     = {Social Media-Controlling},
  series = {Handbuch Marketing-Controlling},
  publisher = {Springer Gabler},
  isbn      = {9783662504055},
  pages     = {191 -- 206},
  language  = {de}
}
@incollection{ZerresDrechslerLitterst,
  author    = {Zerres, Christopher and Drechsler, Dirk and Litterst, Florian},
  title     = {Kennzahlen des Marketingcontrollings},
  series = {Die richtigen Kennzahlen optimal nutzen : Auswahl, Gestaltung, Implementierung, Praxisbeispiele},
  editor    = {Gleich, Ronald and Munck, Jan Christoph},
  publisher = {Haufe Group},
  address   = {Freiburg et al.},
  isbn      = {978-3-648-11417-9},
  pages     = {95 -- 116},
  language  = {de}
}