PSYCHOMETRIC PROPERTIES OF THE NECK DISABILITY INDEX

Objectives: To determine if a response set bias existed, to assess the factor structure and internal consistency, and to compare Neck Disabi lity Index (NDI) scores with visual analogue scale (VAS) scores for pa in intensity. Summary of Background Data: Although neck pain is a comm on problem, few instruments exist to assess the disability that accomp anies it. The NDI is a 10 item paper-and-pencil measure of disability resulting from neck pain. Study Design: A cross sectional study evalua ting the psychometric properties of the NDI. Methods: Seven modified v ersions of the original NDI were developed to assess the presence or a bsence of response set bias using a one-way analysis of variance. Inte rnal consistency was measured by a Cronbach alpha, two factor analyses (exploratory and confirmatory) were conducted to examine the structur e of the NDI and stepwise regression analysis was used to examine the variables most predictive of VAS scores. Results: Results from 237 nec k pain patients show that the responses given on the eight versions of the NDI are a function of the content and not of the format in which the items are presented. The NDI has stable psychometric characteristi cs, evidenced by high internal consistency (alpha =.92). In both facto r analyses, one factor was extracted. Conclusions: The NDI possesses s table psychometric properties and provides an objective means of asses sing the disability of patients suffering from neck pain.