• Marta Pereira, Eduardo Brazete Cruz, Lúcia Domingues, Susana Duarte, Filomena Carnide, and Rita Fernandes.
• *Policlinica do Satao Unip. LDA, Viseu, Portugal†Escola Superior de Saúde, Instituto Politécnico de Setúbal, Setúbal, Portugal‡Centro de Medicina e Reabilitação de Alcoitão, Cascais, Portugal§Universidade Técnica de Lisboa, Faculdade de Motricidade Humana, CIPER, LBMF, Lisboa, Portugal.
• Spine. 2015 Nov 1; 40 (22): E1180-6.

Study DesignA prospective cohort study with a 7-week follow-up of 113 patients with chronic neck pain undergoing physiotherapy.ObjectiveTo examine the responsiveness of the Portuguese Version of the Neck Disability Index (NDI-PT), and to determine the minimal clinically important difference (MCID), minimal detectable change (MDC), and floor/ceiling effects.Summary Of Background DataStudies that determine MDC and MCID are needed to provide more accurate outcome evaluation and critically assess potential relevant sources for differences in the minimal important change values for the NDI.MethodsThe NDI-PT was administered twice: at the baseline and after 7 weeks of physiotherapy treatment. A Global Transition Scale was used as an external criterion measure to distinguish between improved and nonimproved patients' scores between baseline and follow-up. The responsiveness of the NDI-PT was assessed through anchor-based methods (correlation coefficient and receiver operating characteristics curves-ROC curves). The MCID was estimated by the ROC curve method, and the MDC through the standard Error of Measurement (SEM).ResultsThe NDI-PT revealed moderate responsiveness when applied to patients with chronic neck pain undergoing physiotherapy (ρ = 0.328 and area under the curve of 0.595, 95% confidence interval: 0.484-0.706). The MDC achieved 12 points, whereas the MCID was found to be 5.5 points. A complementary ROC analysis based on percentage differences in NDI-PT scores from baseline revealed an optimal cutoff point of 27%. The optimal cutoff point was found to be dependent of disability baseline scores.ConclusionThe NDI-PT demonstrated moderate levels of responsiveness. The amount of change in questionnaire scores perceived by the patient to be meaningful is smaller than the amount of change required to be statistically 95% confident that score change is not just measurement error.Level Of EvidenceN/A.

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