The Short-Form Neck Disability index has adequate measurement properties in chronic neck pain patients

Objectives To assess test-retest reliability, internal consistency, construct validity, and the presence of ceiling and floor effects in the Brazilian version of the Short-Form Neck Disability Index (SF-NDI) in patients with chronic neck pain. Methods One hundred and fifty-six patients answered the Numerical Pain Rating Scale (NPRS), Short-Form Neck Disability Index (SF-NDI), Tampa Scale of Kinesiophobia (TKS), Pain Catastrophizing Scale (PCS), and the 36-Item Short-Form Health Survey questionnaire (SF-36). Another sample (n = 51) filled the SF-NDI at two different times, and test-retest reliability was measured using the intraclass correlation coefficient (ICC), standard error of measurement (SEM), and minimum detectable change (MDC). The internal consistency of the SF-NDI was analyzed by Cronbach's alpha. To determine construct validity, Spearman's correlation coefficient was used to determine the magnitude of the correlation between the score of the SF-NDI and other measurement instruments: NPRS, TKS, PCS, SF-36, and original NDI. Results SF-NDI presented substantial reliability (ICC = 0.844) and adequate internal consistency (Cronbach's alpha = 0.778). We observed significant values and with a correlation magnitude greater than 0.80 for the SF-NDI with the original NDI, between 0.30 and 0.50 for the correlations with TKS, and the functional capacity and pain domains of the SF-36, and less than 0.30 with the other study instruments. No participant reached the maximum score. Ceiling and floor effects were not observed. Conclusions SF-NDI with 5 items has adequate measurement properties in Brazilian chronic neck pain patients.