title: Proposing a Parkinson's disease-specific tremor scale from the MDS-UPDRS.
abstract: BACKGROUND
  This article proposes an International Parkinson and Movement Disorder Society (MDS)-UPDRS tremor-based scale and describes its measurement properties, with a view to developing an improved scale for assessing tremor in Parkinson's disease (PD).
  
  
  METHODS
  This was a cross-sectional, multicenter study of 435 PD patients. Rasch analysis was performed on the 11 MDS-UPDRS tremor items. Construct validity, precision, and test-retest reliability were also analyzed.
  
  
  RESULTS
  After some modifications, which included removal of an item owing to redundancy, the obtained MDS-UPDRS tremor scale showed moderate reliability, unidimensionality, absence of differential item functioning, satisfactory convergent validity with medication, and better precision than the raw sum score. However, the scale displayed a floor effect and a need for more items measuring lower levels of tremor.
  
  
  CONCLUSIONS
  The MDS-UPDRS tremor scale provides linear scores that can be used to assess tremor in PD in a valid, reliable way. The scale might benefit from modifications and studies that analyze its responsiveness.
authors.affiliation: National School of Public Health, Institute of Health Carlos III and REDISSEC, Madrid, Spain.
authors.forename: Maria João
authors.initials: MJ
authors.lastname: Forjaz
authors.affiliation: National School of Public Health, Institute of Health Carlos III, Madrid, Spain.
authors.forename: Alba
authors.initials: A
authors.lastname: Ayala
authors.affiliation: Parkinson's and Movement Disorders Center and Department of Neurology, Virginia Commonwealth University, Richmond, Virginia, USA.
authors.forename: Claudia M
authors.initials: CM
authors.lastname: Testa
authors.affiliation: Imperial College, Clinical Neuroscience, London, United Kingdom.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Bain
authors.affiliation: Department of Neurology, Southern Illinois University School of Medicine, Springfield, Illinois, USA.
authors.forename: Rodger
authors.initials: R
authors.lastname: Elble
authors.affiliation: Department of Neurology, Medical University of Vienna, Vienna, Austria.
authors.forename: Dietrich
authors.initials: D
authors.lastname: Haubenberger
authors.affiliation: National Center of Epidemiology and CIBERNED, Institute of Health Carlos III, Madrid, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: Rodriguez-Blazquez
authors.affiliation: Department of Neurology, Christian-Albrechts University, Kiel, Germany.
authors.forename: Günther
authors.initials: G
authors.lastname: Deuschl
authors.affiliation: National Center of Epidemiology and CIBERNED, Institute of Health Carlos III, Madrid, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: Martinez-Martin
mesh_terms: D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000150:complications / Q000175:diagnosis*; D011594:Psychometrics / Q000295:instrumentation*; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D014202:Tremor / Q000175:diagnosis* / Q000209:etiology
keywords: MDS-UPDRS; Parkinson's disease; Rasch analysis; tremor