The Neck Pain Driving Index (NPDI) for chronic whiplash-associated disorders: development, reliability, and validity assessment.
BACKGROUND CONTEXT
Driving is a functional complaint of many individuals with chronic whiplash-associated disorders (WAD). Current driving scales do not include the most troublesome driving tasks for this group, which suggests that a new tool is required to assess perceived driving difficulty in this population.


PURPOSE
To develop a Neck Pain Driving Index (NPDI) to assess the degree of perceived driving difficulty for individuals with chronic WAD and evaluate the reliability and validity of the NPDI.


STUDY DESIGN
Descriptive/survey.


PATIENT SAMPLE
An external panel of 15 researchers/clinicians and 87 participants with chronic WAD.


OUTCOME MEASURES
The NPDI and a 0 to 10 numeric rating scale (NRS) of perceived driving difficulty (0, no difficulty and 10, maximum difficulty).


METHODS
Phase 1 included the construction of a preliminary NPDI and content validity assessment of question items by a 15-member external panel. Comprehension was evaluated by seven participants with chronic WAD. In Phase 2, the final version of the NPDI was developed via descriptive analysis and assessment of internal consistency using responses of 87 participants with chronic WAD. Subsequently, the convergent validity was assessed using NRS scores. Test-retest reliability at 1 month was investigated in 25 of the 87 participants. Psychometric properties of the driving tasks in the final NPDI were categorized by the external panel, based on the hierarchal Michon model of driving task performance levels. An additional symptom section was developed to better understand the reasons for driving difficulties.


RESULTS
The final NPDI included 12 driving tasks, which scored at least 80% on the content validity index (CVI), ensuring content validity. The NPDI demonstrated good internal consistency (α=0.80), convergent validity (ρ=0.51; p<.01), and test-retest reliability (intraclass correlation coefficient, 0.73; p<.01). As a result of the assessment of psychometric properties, driving tasks were categorized into the strategic (n=3), tactical (n=7), and operational (n=2) levels in the Michon model. The content validity of 11 symptoms (CVI ≥80%) was established by the external panel.


CONCLUSIONS
The NPDI was developed to assess the degree of perceived driving difficulty in the chronic whiplash population. Reliability and validity of the NPDI were ensured. The NPDI can be the entry point for discussions on driving difficulties between clinicians and patients with chronic WAD.