Development of a short version of the Neck Pain and Disability Scale

Previous evaluations of the 20-item Neck Pain and Disability Scale (NPAD) were indicative of excessive redundancy of the measure. The aim of this study was to develop a shortened version of the NPAD (sf-NPAD) based on results of item-to-total-score correlations and factor analysis as published by the developers of the original NPAD. Two items with the highest item-to-total score correlation were selected per factor subscale with the exception of one factor consisting of only one item. This resulted in the selection of 9 items for the sf-NPAD. The sf-NPAD was validated in a separate sample of 448 neck pain patients from 15 general practices in the area of Gottingen/Germany. Participants completed the 20-item NPAD German version and gave additional sociodemographic and clinical information. Psychometric properties of the sf-NPAD were evaluated using Cronbach's alpha, item-to-total-score correlation, and unrestricted principal factor analysis. Construct validity was evaluated by Pearson's r with clinical characteristics. Discriminative validity was examined by comparing differences between subgroups stratified by psychosocial characteristics using t-tests for mean scores. Cronbach's alpha of the sf-NPAD was 0.88. Item-to-total-scale correlations ranged between 0.628 and 0.815, and sf-NPAD items homogeneously loaded on a single factor. Correlation analysis showed high correlations with criterion variables. The sf-NPAD scores of patient subgroups were significantly different showing good discriminative validity. In conclusion, the sf-NPAD demonstrated good validity and internal consistency in this general practice setting. The abbreviated version may facilitate applicability of the scale in clinical and research settings.