title: Validation of the German version of the Neck Disability Index (NDI).
abstract: BACKGROUND
  The Neck Disability Index (NDI) is the most commonly used outcome measure for neck pain. This study aimed to determine the psychometric properties of a German version of the NDI. Cross-cultural translation and psychometric testing of the NDI were performed.
  
  
  METHODS
  The 10-item NDI was translated into German and administered to 558 patients with chronic unspecific neck pain (Mean age 49.9 ± 11.4 years, 76% female). The factor structure and reliability of the NDI were assessed using factor analysis, Cronbach's alpha, split-half reliability (Spearman-Brown coefficient), and intra-class correlation (ICC2,1). To determine convergent validity, pain intensity (visual analog scale; VAS), pain on movement (VAS), and quality of life (Short Form 36 Health Survey Questionnaire; SF-36) were correlated with the NDI. Correlation with range of motion and sensitivity to change were also assessed in a subsample of 49 patients.
  
  
  RESULTS
  The mean NDI score was 32.75 ± 13.09. Factor analysis revealed a single factor that explained 39.8% of the variance. Cronbach's alpha was 0.81; Spearman-Brown coefficient was 0.80; and intra-class correlation was 0.81 (95% confidence interval = 0.78, 0.83). Significant correlations were found for pain intensity (r = 0.22, p < 0.01), pain on movement (r = 0.39, p < 0.01), quality of life (r = -0.30 to -0.45, p < 0.01), and range of motion (r = -0.34, p = 0.02). Patients who reported global improvement of health after an exercise or yoga intervention showed a higher decrease on the NDI than patients who reported no global improvement (p < 0.01).
  
  
  CONCLUSIONS
  The German version of the NDI has a comparable factor structure as the original version, acceptable psychometric properties, and is sensitive to change after physical activity. Neck disability is associated with other measures of neck pain.
authors.affiliation: Department of Internal and Integrative Medicine, Kliniken Essen-Mitte, Faculty of Medicine, University of Duisburg-Essen, Am Deimelsberg 34a, 45276 Essen, Germany. h.cramer@kliniken-essen-mitte.de.
authors.forename: Holger
authors.initials: H
authors.lastname: Cramer
authors.forename: Romy
authors.initials: R
authors.lastname: Lauche
authors.forename: Jost
authors.initials: J
authors.lastname: Langhorst
authors.forename: Gustav J
authors.initials: GJ
authors.lastname: Dobos
authors.forename: Andreas
authors.initials: A
authors.lastname: Michalsen
mesh_terms: D000328:Adult; D059350:Chronic Pain / Q000175:diagnosis* / Q000523:psychology; D004185:Disability Evaluation; D005858:Germany; D019416:Head Movements; D006801:Humans; D007802:Language; D008875:Middle Aged; D019547:Neck Pain / Q000175:diagnosis* / Q000523:psychology; D010147:Pain Measurement; D011594:Psychometrics; D011788:Quality of Life; D016032:Randomized Controlled Trials as Topic / Q000706:statistics & numerical data; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D014175:Translating