title: Responsiveness and Interpretability of the Portuguese Version of the Neck Disability Index in Patients With Chronic Neck Pain Undergoing Physiotherapy.
abstract: METHODS
  A prospective cohort study with a 7-week follow-up of 113 patients with chronic neck pain undergoing physiotherapy.
  
  
  OBJECTIVE
  To 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.
  
  
  BACKGROUND
  Studies 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.
  
  
  METHODS
  The 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).
  
  
  RESULTS
  The 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.
  
  
  CONCLUSIONS
  The 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.
  
  
  METHODS
  N/A.
authors.affiliation: *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.
authors.forename: Marta
authors.initials: M
authors.lastname: Pereira
authors.forename: Eduardo Brazete
authors.initials: EB
authors.lastname: Cruz
authors.forename: Lúcia
authors.initials: L
authors.lastname: Domingues
authors.forename: Susana
authors.initials: S
authors.lastname: Duarte
authors.forename: Filomena
authors.initials: F
authors.lastname: Carnide
authors.forename: Rita
authors.initials: R
authors.lastname: Fernandes
mesh_terms: D000328:Adult; D000368:Aged; D059350:Chronic Pain / Q000628:therapy*; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D019547:Neck Pain / Q000175:diagnosis* / Q000628:therapy*; D010147:Pain Measurement; D026741:Physical Therapy Modalities; D011446:Prospective Studies; D012720:Severity of Illness Index; D016896:Treatment Outcome