Measurement invariance of the Illness

3 Department of Personality, Evaluation and Psychological Treatment, University of Granada, Granada, Spain, 4 Department of Clinical Psychology and Psychotherapy, Philipps University Marburg, Marburg, Germany, 5 Department Medical Service III and Rheumatology, University Hospital Coimbra, Coimbra, Portugal, 6 Department of Experimental Clinical and Health Psychology, Ghent University, Ghent, Belgium, 7 Department of Developmental and Clinical Psychology, Tilburg University, Tilburg, Netherlands, 8 Department of Psychology, Wayne State University, Detroit, USA, 9 Department of Medical Psychology, Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands, 10 Department of Rheumatology & Clinical Immunology, University Medical Center Utrecht, Utrecht, Netherlands.