@article{KellmannBeckmann2003,
  author    = {Kellmann, Michael and Beckmann, J{\"u}rgen},
  title     = {Sport und Entspannungsverfahren},
  year      = {2003},
  language  = {de}
}
@article{BeckmannKellmann2003,
  author    = {Beckmann, J{\"u}rgen and Kellmann, Michael},
  title     = {Procedures and principles of sportpsychological assessment},
  year      = {2003},
  language  = {en}
}
@article{KellmannBeckmann2003,
  author    = {Kellmann, Michael and Beckmann, J{\"u}rgen},
  title     = {Research and intervention in sport psychology : new perspectives for an inherent conflict},
  year      = {2003},
  language  = {en}
}