title: Exploring the Validity of the Short Version of the Problem Behaviours Assessment (PBA-s) for Huntington's disease: A Rasch Analysis.
abstract: BACKGROUND
  The short version of the Problem Behaviours Assessment (PBA-s) is the recommended outcome measure for behavioural symptoms in Huntington's disease. Rasch analysis was used to further investigate the measurement limitations of the PBA-s.
  
  
  OBJECTIVE
  1) To assess the psychometric properties of the 11 severity and frequency items within the PBA-s and 2) to determine the construct validity of using a total PBA-s score as a clinical outcome measure.
  
  
  METHODS
  PBA-s data for 517 participants from Enroll-HD were included in the Rasch analysis. Separate analyses were conducted for the severity and frequency items of the PBA-s, using RUMM2030 software. Achieving fit to the model provides supporting evidence that all items contribute to a single underlying latent trait. This property is defined as internal construct validity.
  
  
  RESULTS
  The total PBA-s severity score demonstrated several important limitations, including disordered response categories for all 11 severity items, local dependency and poor targeting. However, modifying the original five-point scoring system to a four-point system resulted in ordered response categories for seven of the severity items and achieved a good overall fit to the Rasch model. For the total PBA-s frequency score, fit to the model was not achieved even after amendments to the scoring system.
  
  
  CONCLUSIONS
  This study suggests that with reduction to a four-point scoring system, the total PBA-s severity score may be considered a valid clinical outcome measure. This study also suggests limitations in the use of a total PBA-s frequency score.
authors.affiliation: College of Medical and Dental Sciences, University of Birmingham, UK.
authors.forename: George
authors.initials: G
authors.lastname: McNally
authors.affiliation: Department of Neuropsychiatry, The Barberry, Birmingham, UK.
authors.forename: Hugh
authors.initials: H
authors.lastname: Rickards
authors.affiliation: Academic Department of Rehabilitation Medicine, Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds, Leeds, UK.
authors.forename: Mike
authors.initials: M
authors.lastname: Horton
authors.affiliation: Faculty of Medicine and Human Sciences, Institute of Human Development, University of Manchester and Manchester Academic Health Science Centre, Manchester, UK.
authors.forename: David
authors.initials: D
authors.lastname: Craufurd
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D006816:Huntington Disease / Q000523:psychology*; D008297:Male; D008875:Middle Aged; D015337:Multicenter Studies as Topic; D000066553:Problem Behavior / Q000523:psychology*; D011594:Psychometrics / Q000379:methods*; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires / Q000592:standards*; D055815:Young Adult
keywords: Enroll-HD; Huntington’s disease; Problem Behaviours Assessment; Rasch; psychometrics