Implementation of the Minimum Clinically Important Difference for the Neck Disability Index Is Often Problematic: A...

Area of Science:

• Clinical assessment and measurement
• Rehabilitation science
• Evidence-based practice

Background:

• The Neck Disability Index (NDI) is a common patient-reported outcome measure.
• The NDI is scored out of 50, but sometimes reported out of 100.
• The Minimally Important Clinical Difference (MCID) for the NDI is typically 7.5/50, but implementation can be inconsistent.

Purpose of the Study:

• To assess the frequency of correct and incorrect application of the MCID for the NDI.
• To identify factors associated with appropriate MCID implementation in research studies.

Main Methods:

• Systematic review of studies citing the NDI MCID.
• Defined appropriate implementation as matching NDI scale and MCID scale.
• Used multivariable logistic regression to analyze study characteristics.

Main Results:

• Of 163 studies, only 24% implemented the NDI MCID appropriately.
• 40% used a 0-100 scale for NDI, and 42% did not report the MCID value.
• Inappropriate (10%) and uncertain (66%) implementations were frequent.

Conclusions:

• Inappropriate and uncertain MCID implementation for the NDI is a significant issue.
• Researchers and clinicians should carefully check scale congruence when interpreting NDI results.
• More recent studies and RCTs showed better MCID implementation.