title: Defining the clinically meaningful difference in gait speed in persons with Parkinson disease.
abstract: OBJECTIVE
  Gait dysfunction is a common target for pharmacological, behavioral, and surgical interventions in persons with Parkinson disease. However, the responsiveness of gait speed, that is, clinically important difference, is not well described in the literature for this population. The purpose of this study was to determine the magnitude of meaningful difference in gait speed using multiple methods of assessment and utilizing a large sample of participants inclusive of various stages of disease severity.
  
  
  METHODS
  Gait speed was measured using an instrumented walkway in 324 ambulatory persons with idiopathic Parkinson disease. Cross-sectional analysis of the clinically important difference for gait speed was performed using distribution- and anchor-based approaches: disability (Schwab and England Activities of Daily Living Scale), disease stage (Modified Hoehn and Yahr Scale), and severity (Unified Parkinson's Disease Rating Scale).
  
  
  RESULTS
  Using distribution-based analyses and effect size metrics, the small important difference in gait speed was 0.06 m/s, moderate was 0.14 m/s, and large was 0.22 m/s. Applying previously established cut-points for small, moderate, and large change in the motor scale score, the associated changes in gait speed that might be expected are 0.02, 0.06, and 0.10 m/s.
  
  
  CONCLUSIONS
  Our data revealed that the clinically important difference in gait speed among persons with Parkinson disease on medication ranged from 0.05 m/s to 0.22 m/s by distribution-based analysis and ranged from 0.02 m/s to 0.18 m/s per level within the anchor-based metrics. These data will aid in evaluating the effectiveness of interventions to improve gait speed in persons with Parkinson disease.Video Abstract available. See video (Supplemental Digital Content 1, http://links.lww.com/JNPT/A77) for more insights from the authors.
authors.affiliation: Department of Applied Physiology and Kinesiology (CJH, JS), Center for Movement Disorders and Neurorestoration, Department of Neurology, (CJH, MM, JS, IAM, AWS, NM, MSO), Department of Physical Therapy (MB), University of Florida, Gainesville; and Department of Kinesiology, Iowa State University, Ames (ELS).
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Hass
authors.forename: Mark
authors.initials: M
authors.lastname: Bishop
authors.forename: Mariana
authors.initials: M
authors.lastname: Moscovich
authors.forename: Elizabeth L
authors.initials: EL
authors.lastname: Stegemöller
authors.forename: Jared
authors.initials: J
authors.lastname: Skinner
authors.forename: Irene A
authors.initials: IA
authors.lastname: Malaty
authors.forename: Aparna
authors.initials: A
authors.lastname: Wagle Shukla
authors.forename: Nikolaus
authors.initials: N
authors.lastname: McFarland
authors.forename: Michael S
authors.initials: MS
authors.lastname: Okun
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D003430:Cross-Sectional Studies; D004185:Disability Evaluation; D005260:Female; D005684:Gait; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000503:physiopathology / Q000534:rehabilitation*; D016896:Treatment Outcome; D016138:Walking / Q000502:physiology*