Purpose: To investigate the validity of the Neck Pain and Disability Scale Dutch Language Version (NPAD-DLV) and the Neck Disability Index (NDI)-DLV.
Methods: NPAD-DLV, NDI-DLV, Short-Form-36 Health Survey (SF-36)-DLV, visual analog scale (VAS)(pain) and VAS(disability) were administered to 112 patients with non-specific chronic neck pain in an outpatient tertiary rehabilitation setting. Twenty seven hypotheses were formulated regarding validity. NPAD-DLV and NDI-DLV were evaluated for content validity (normal distribution total scores, missing items, floor and ceiling effects), internal consistency (Cronbach's alpha and Spearman Item-total correlations), construct validity (Pearson correlations with SF-36 domains, VAS(pain) and VAS(disability) and Pearson correlation between total scores of NPAD-DLV and NDI-DLV).
Results: NPAD-DLV and NDI-DLV scores were distributed normally. Missing items were negligible. Floor and ceiling effects were absent in NPAD-DLV and in NDI-DLV two items had floor effects and one item had a ceiling effect. Cronbach's alpha of NPAD-DLV was 0.93 and of NDI-DLV 0.83. Item-total correlations ranged for NPAD-DLV from 0.45 to 0.73 and for NDI-DLV from 0.40 to 0.64. The correlation between, respectively, NPAD-DLV and NDI-DLV and: SF-36 domains ranged from -0.36 to -0.70 and from -0.34 to -0.63; VAS(pain) was 0.54 and 0.43; VAS(disability) was 0.57 and 0.52. The correlation between the total scores of NPAD-DLV and NDI-DLV was 0.77. Twenty six hypotheses were not rejected and one hypothesis was rejected.
Conclusion: The NPAD-DLV and NDI-DLV are valid measures of self-reported neck-pain related disability.