title: Psychometric study of the Persian short-form eight-item Parkinson's disease questionnaire (PDQ-8) to evaluate health related quality of life (HRQoL).
abstract: BACKGROUND
  To assess validation and reliability of the Persian version of the short-form 8-item Parkinson's disease questionnaire (PDQ-8) and to compare its psychometric properties with that of the long-form questionnaire (PDQ-39) in order to evaluate the health-related quality of life (HRQoL) in patients with Parkinson's disease (PD).
  
  
  METHODS
  This cross-sectional study was conducted on 114 non-demented idiopathic PD (IPD) patients consecutively recruited from an outpatient referral movement disorder clinic. Patients were interviewed to fill in the Persian version of PDQ-39 and PDQ-8 questionnaires and clinical examination was performed to measure disease severity indices.
  
  
  RESULTS
  The Cronbach's alpha coefficient of the entire PDQ-8 was 0.740 (95% CI: 0.661-0.806). Replacement of PDQ-8 items with other questions with the highest internal consistency within each dimension of the original PDQ-39 did not improve Cronbach's alpha coefficient [0.723 (95% CI: 0.639-0.794)]. The scores from both PDQ-8 and PDQ-39 had significant correlation with the Hoehn & Yahr (rPDQ-8 = 0.376, rPDQ-39 = 0.442), and Schwab & England (rPDQ-8 = -0.503, rPDQ-39 = -0.598) disease severity scales and disease duration (rPDQ-8 = 0.342, rPDQ-39 = 0.396).
  
  
  CONCLUSIONS
  Persian version of the short-form PDQ (PDQ-8) was shown to be a valid and reliable instrument to assess disease-specific HRQoL in a PD population when used independently. Although the PDQ-8 items were not necessarily those with the highest internal consistency in the components of PDQ-39, they entirely showed proper psychometric properties especially in mental and behavioral aspects. PDQ-8 is a practical and informative instrument in daily clinical practice where clinicians are in shortage of time and when a validated self-reported brief questionnaire is of value.
authors.affiliation: Division of Clinical geriatrics, Department of Neurobiology, Care Sciences, and Society (NVS), Karolinska Institutet, Stockholm, Sweden. sm.fereshtehnejad@ki.se.
authors.forename: Seyed-Mohammad
authors.initials: SM
authors.lastname: Fereshtehnejad
authors.forename: Nader
authors.initials: N
authors.lastname: Naderi
authors.forename: Arash
authors.initials: A
authors.lastname: Rahmani
authors.forename: Gholam Ali
authors.initials: GA
authors.lastname: Shahidi
authors.forename: Ahmad
authors.initials: A
authors.lastname: Delbari
authors.forename: Johan
authors.initials: J
authors.lastname: Lökk
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003430:Cross-Sectional Studies; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D007492:Iran; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000175:diagnosis* / Q000523:psychology; D011594:Psychometrics; D011788:Quality of Life / Q000523:psychology; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires