@conference{17559,
  author = {Ostelo R. and Hancock M. and de Vet H. and Knol D. and Kamper S. and Maher C.},
  title = {Reliability and validity of global perceived effect scales},
  year = {2009},
  journal = {Boston International Forum X: Primary Care Research on Low Back Pain},
  address = {Boston, USA},
  language = {eng},
}