title: Validation of an ambulatory capacity measure in Parkinson disease: a construct derived from the Unified Parkinson's Disease Rating Scale.
abstract: BACKGROUND
  A construct calculated as the sum of items 13-15, 29, 30 of the Unified Parkinson's Disease Rating Scale (UPDRS) has been used as an "Ambulatory Capacity Measure" (ACM) in Parkinson disease (PD). Its construct validity has never been examined. A similar construct, consisting of the mean value of the same UPDRS items has been used under the acronym PIGD as a measure of postural instability and gait disorder in PD.
  
  
  OBJECTIVE
  To examine the construct validity of the ACM and PIGD in PD.
  
  
  METHODS
  We analyzed data in an existing database of 340 PD patients, Hoehn and Yahr stages (HYS) 1-5 who participated in a study of falls. Number of falls (NOF) was recorded over 4 weeks, and UPDRS (mental, ADL, and motor subscales), HYS, Activities Based Confidence Scale (ABC), Freezing of Gait Questionnaire (FOG), Five Times Sit-to-Stand (FTSS), Timed Up-and Go (TUG), Gait Velocity (GV), and Berg Balance Scale (BBS) evaluations were performed. Internal consistency was assessed by Cronbach's alpha. Construct validity was assessed through correlations of the ACM and PIGD to these measures and to their summed-ranks. A coefficient of determination was calculated through linear regression.
  
  
  RESULTS
  Mean age was 71.4, mean age at diagnosis 61.4 years; 46% were women; mean UPDRS subscale scores were: Mental 3.7; ADL 15.7; motor: 27.1; mean ACM was 6.51, and mean PIGD 1.30. Cronbach's alpha was 0.78 for both ACM and PIGD. Spearman correlation coefficients between the ACM/PIGD and ABC, FOG, TUG, GV and BBS were 0.69, 0.72, 0.67, 0.58, and 0.70 respectively. Correlation between the ACM/PIGD and summed-ranks of HYS, NOF, ABC, FOG, FTSS, TUG, GV and BBS was high (Spearman r = 0.823, p < 0.0001); 68% of the variability in the summed-ranks was explained by ACM/PIGD.
  
  
  CONCLUSIONS
  The ACM and the PIGD are valid global measures and accurately reflect the combined effects of the various components of ambulatory capacity in PD patients with HY stages 1-4.
authors.affiliation: Struthers Parkinson's Center, Golden Valley, MN, USA.
authors.forename: Sotirios A
authors.initials: SA
authors.lastname: Parashos
authors.affiliation: Department of Public Health Sciences, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: Jordan
authors.initials: J
authors.lastname: Elm
authors.affiliation: Department of Neurological Sciences, University of Vermont, Burlington, VT, USA.
authors.forename: James T
authors.initials: JT
authors.lastname: Boyd
authors.affiliation: Department of Neurology and Neurosurgery, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Kelvin L
authors.initials: KL
authors.lastname: Chou
authors.affiliation: Department of Public Health Sciences, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Dai
authors.affiliation: Department of Neurology and Neurosurgery, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Mari
authors.affiliation: Department of Neurology, Georgia Regents University, Augusta, GA, USA.
authors.forename: John C
authors.initials: JC
authors.lastname: Morgan
authors.affiliation: Department of Neurology, Brigham & Women's Hospital, Boston, MA, USA.
authors.forename: Lewis
authors.initials: L
authors.lastname: Sudarsky
authors.affiliation: Struthers Parkinson's Center, Golden Valley, MN, USA.
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Wielinski
mesh_terms: D000058:Accidental Falls; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D005239:Fear / Q000523:psychology; D005260:Female; D020233:Gait Disorders, Neurologic / Q000175:diagnosis* / Q000209:etiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000150:complications* / Q000523:psychology; D015203:Reproducibility of Results; D012678:Sensation Disorders / Q000175:diagnosis* / Q000209:etiology*; D012720:Severity of Illness Index; D018709:Statistics, Nonparametric
keywords: Idiopathic Parkinson disease; PIGD; ambulation; ambulatory capacity; balance; falls; scales