title: Unidimensionality of the Elderly Mobility Scale in older acute medical patients: different methods, different answers.
abstract: OBJECTIVE
  To investigate the unidimensionality of the Elderly Mobility Scale (EMS) in an older acute medical population.
  
  
  METHODS
  EMS data were collected within 48 hours of hospital admission and discharge, respectively, from consecutive older acute medical patients. Rasch and factor analysis of EMS data were conducted.
  
  
  METHODS
  Acute tertiary hospital, South Australia.
  
  
  RESULTS
  Factor analysis identified a two-factor solution for both admission and discharge EMS data. At hospital admission (n=120), EMS data fitted the Rasch model (χ(2)=18.31, P=0.19, df=14). One item, the timed walk test, had a high positive fit residual (+3.93). At hospital discharge (n=105), EMS data did not fit the Rasch model (χ(2)=25.66, P=0.03, df=14). Item and person scores were not well matched because of a ceiling effect in discharge EMS scores. The functional reach item showed some misfit to the Rasch model and the gait item had a disordered threshold. After rescoring this disordered threshold, discharge EMS data fitted the Rasch model.
  
  
  CONCLUSIONS
  Conflicting results were identified using a classical test theory and item response theory approach. Although the EMS fitted the Rasch model, an unacceptable ceiling effect at hospital discharge limits the validity of the EMS for measuring and monitoring the mobility of older acute medical patients in the hospital setting.
authors.affiliation: Musculoskeletal Research Centre & School of Physiotherapy, La Trobe University, Bundoora, Victoria 3083, Australia. n.demorton@latrobe.edu.au
authors.forename: Natalie A
authors.initials: NA
authors.lastname: de Morton
authors.forename: Jo S
authors.initials: JS
authors.lastname: Nolan
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D000369:Aged, 80 and over; D004185:Disability Evaluation; D005163:Factor Analysis, Statistical; D005260:Female; D006760:Hospitalization; D006801:Humans; D008124:Locomotion / Q000502:physiology*; D008297:Male; D051346:Mobility Limitation; D017063:Outcome Assessment, Health Care; D026741:Physical Therapy Modalities; D013021:South Australia