Agreement between original and Rasch-approved neck disability index

Area of Science:

• Orthopedics
• Rehabilitation Medicine
• Health Outcomes

Background:

• The Neck Disability Index (NDI) is widely used for neck pain assessment.
• Modified NDI versions exist to address measurement deficits.
• The traditional 10-item NDI remains the most common version.

Purpose of the Study:

• To assess agreement between traditional and Rasch-based Neck Disability Index versions.
• To understand score differences arising from using different NDI versions.

Main Methods:

• Secondary data analysis of prospectively collected data.
• Literature search for Rasch-approved NDI versions.
• Bland-Altman plots to analyze agreement between NDI versions.

Main Results:

• Two Rasch-approved NDI versions (8-item and 5-item) were identified.
• Mean score differences were observed between the 10-item and 5-item NDI (-4.6 points).
• Wider limits of agreement were found between the 10-item and 8-item/5-item NDI versions.

Conclusions:

• Rasch-based NDI versions offer interval-level scoring, unlike the ordinal traditional NDI.
• Substantial score differences exist between Rasch-based and traditional NDI versions.
• Different NDI versions should not be used interchangeably due to bias.