Validity and reliability of a German version of the Neck Disability Index (NDI-G).
The Neck Disability Index (NDI) is a widely used questionnaire in the assessment of disability of neck patients. The aim of this study was to translate the NDI according to established guidelines into German (NDI-G) and to test the psychometric properties. Patients with acute (ACU) and chronic neck pain (CHR) and a healthy control group (HCG) completed the NDI-G twice with a mean test-retest interval of 3 days. The total score of NDI-G showed high reliability (Intraclass correlation coefficient (ICC2,1) = 0.92) and a high Cronbach's alpha (α = 0.96). The minimal detectable change was 7 points. The Bland-Altman plot revealed a small positive systematic error of 1.02 points. The Kruskal-Wallis test showed significant differences in the NDI-G total score among the three groups (χ(2) = 29.77, p < 0.001). Mann-Whitney U tests showed significant differences in the total score between ACU and HCG (p < 0.001), and CHR and HCG (p < 0.001). The factor analysis of NDI-G yielded 2 factors that together explained 67% of the variance. Spearman's phi coefficients showed no correlation between the NDI-G total score and the visual analogue scale (VAS) in the ACU group (phi = 0.23, p = 0.40), and a moderate correlation in the CHR group (phi = 0.55, p = 0.03). The item analysis of the NDI-G revealed moderate to good reliability for all items. Only the item 'work' could differentiate between the ACU and CHR group. The NDI-G emerged from this study as a valid and reliable assessment. Its psychometric properties are comparable with the original version. Thus, the NDI-G is recommended for research and clinical settings in neck pain in German speaking countries.
Department of Physiotherapy, Balgrist University Hospital, Zurich, Switzerland; Physiotherapy and Occupational Therapy Research, Directorate of Research and Education, University Hospital Zurich, Switzerland. Electronic address: jaap.swanenburg@balgrist.ch.
Jaap
J
Swanenburg
Department of Chiropractic Medicine, University Hospital of Balgrist, Zürich, Switzerland.
Kim
K
Humphreys
Department of Physiotherapy, Balgrist University Hospital, Zurich, Switzerland; Department of Chiropractic Medicine, University Hospital of Balgrist, Zürich, Switzerland.
Anke
A
Langenfeld
Department of Physical Medicine and Rheumatology, Balgrist University Hospital, Zurich, Switzerland.
Florian
F
Brunner
Institute of Human Movement Sciences and Sport, ETH Zurich, Switzerland.
Brigitte
B
Wirth
D000208:Acute Disease; D000328:Adult; D016022:Case-Control Studies; D002574:Cervical Vertebrae / Q000503:physiopathology*; D002908:Chronic Disease; D004185:Disability Evaluation; D005260:Female; D005858:Germany; D006801:Humans; D008297:Male; D008875:Middle Aged; D019547:Neck Pain / Q000175:diagnosis*; D011594:Psychometrics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D014177:Translations; D055815:Young Adult
NDI; Neck; Pain; Reliability; Validity