The spine journal : official journal of the North American Spine Society
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Randomized Controlled Trial Multicenter Study
The development of a model for translation of the Neck Disability Index to utility scores for cost-utility analysis in cervical disorders.
The Neck Disability Index (NDI) is a commonly used disease-specific instrument for cervical spine disorders with good responsiveness and psychometric properties compared with general health status measures. However, NDI scores are unitless and do not have an intrinsic value that is comparable to other health status measures, and these scores have limited value in cost-utility analysis. The translation of disease-specific measures to Short Form-6 Dimensions (SF-6D) utility scores may be useful in cost-utility analysis. ⋯ Correlations between NDI and SF-6D utility scores are strong and statistically significant. The model has a large R(2) and small RMSE. The prediction models produce a small mean prediction error, but the SD of the prediction errors is large. High correlations between NDI and SF-6D permit these models to be used to calculate overall utilities, changes in utilities, and quality-adjusted life-years for large data samples. However, the relatively large observed prediction error SDs may limit the accuracy of translation of individual data points or small sample sizes.