Clinimetric properties of the Turkish translation of a modified neck disability index

Neck pain is a common problem that can greatly affect a person's activities of daily living. Functional status questionnaires are important in assessing this effect, and are used to follow up neck pain management programs. The Neck Disability Index (NDI) is the first-created scale for neck pain-related disability and is widely translated and in common used in many countries. Our aim is investigate to clinometric properties of a Turkish version of modified NDI and to give a choice in daily practise of versions to be used.

The modified NDI was applied to 30 patients for reliability. 185 patients participated in the validity study. All patients were recruited from the outpatient clinic of our department. The scale was translated by the forward and backward translation procedure according to the COSMIN criteria. The test was repeated at 48 hours interval for reliability study. SPSS-10.0, software was used for statistical analyses. The Intraclass correlation coefficient was used for the test- retest reliability of the modified NDI. Cronbach α was used for internal consistency. Factor analysis was used for construct validity. The validity of the modified NDI with respect to the SF-36, HAD, VAS pain, VAS disability was assessed using Spearman correlations.

The Intraclass correlation coefficient between first and second (within 48 hours) evaluation of test (rs) was 0.92. Questions 1,4,6,8,10 were shown to have excellent reliability. (rs > 0.9). Question 10 was the most frequently challenged question because "recreational and social activities" do not have not the same meanings in Turkey than in western countries. This required that detailed explanations be provided by the investigators. Cronbach's alpha for the total index was 0.88. A single factor accounting for 80.2% of the variance was obtained. Validity studies demonstrated good and moderate correlations (rs) among NDI, HAD, VAS, physical function subtitle of SF 36 (0.62, 0.76, 0.68).

The modified NDI-Turkish version is a reliable and valid test and is suitable for daily practise.