Study design: Study of two cohorts with a differing severity of disease before and after treatment.
Objectives: The aim of this study was to examine the validity and sensitivity to change of the German version of the cervical NASS patient questionnaire.
Summary of background data: To the authors' best knowledge, there are no data revealing the psychometric properties of the cervical NASS patient questionnaire.
Patients and methods: The validity and sensitivity in patients with cervical spine disorders who were referred by their physician either to an inpatient rehabilitation program or to an outpatient physiotherapy were examined. They were consecutively recruited. Their functioning and health status were assessed when entering the study and after the treatment by the NASS questionnaire and the Medical Outcome Survey Short Form-36 (SF-36).
Results: Criterion validity was demonstrated by the statistically significant correlations between the NASS subscores and all subscores of SF-36. As expected, the SF-36 subscores Physical Function and Pain showed the strongest associations to the NASS subscore Pain and Disability (rho = 0.75 and 0.65, respectively), demonstrating construct validity of the latter. Discriminative validity of NASS subscores was shown in two ways. First, a statistically significant difference was found between functional and health status of the two cohorts with better scores in the patients referred to outpatient physiotherapy as compared with those sent to an inpatient rehabilitation program. Second, statistically significant and clinically important improvements recorded by the NASS subscores were demonstrated in both patient groups after the treatment in accordance with improved SF-36 subscores. Moreover, the NASS subscores demonstrated good sensitivity to change (Pain and Disability with a standard response mean ranging from 0.64 to 1.24).
Conclusions: The German version of the cervical NASS patient questionnaire (NASS) is a valid instrument for patients with cervical spine health problems. As this instrument is also sensitive to change, it is recommended for use. Moreover, the present study gives evidence for the validity of the original cervical NASS questionnaire in English.