title: Classifying Whiplash Recovery Status Using the Neck Disability Index: Optimized Cutoff Points Derived From Receiver Operating Characteristic.
abstract: OBJECTIVE
  Researchers often use Neck Disability Index (NDI) scores to classify recovery status in whiplash patients. The purpose of this study was to investigate the optimal cutoff point score for the NDI as a mechanism for differentiating recovery from nonrecovery after whiplash.
  
  
  METHODS
  Subjects (N = 123) who had previously sustained whiplash injuries were recruited from 12 clinics. Subjects rated themselves as being recovered (36%) or nonrecovered (64%). This state variable was compared with their NDI score as test variable using the receiver operating characteristic statistic. The area under the receiver operating characteristic curve and optimized cutoff points were computed for the whole group and also dichotomized for sex and age.
  
  
  RESULTS
  The mean NDI score for the recovered group was 7.8. It was 27.1 for the nonrecovered group. The cutoff point that optimized sensitivity and specificity for the whole group was an NDI score of 15. For women, it was 19; for older persons, it was 21.
  
  
  CONCLUSIONS
  The optimal NDI score cutoff point for differentiating the recovery state after whiplash is 15. Misclassification errors are likely when using lower values.
authors.affiliation: Director, Spine Research Institute of San Diego, San Diego, CA.
authors.forename: Arthur C
authors.initials: AC
authors.lastname: Croft
authors.affiliation: Private Practice, Richland, WA.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Workman
authors.affiliation: Private Practice, Brookfield, WI.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Szatalowicz
authors.affiliation: Private Practice, Fort Smith, AR.
authors.forename: Philip E
authors.initials: PE
authors.lastname: Roberts
authors.affiliation: Private Practice, Ballwin, MO.
authors.forename: Leonard R
authors.initials: LR
authors.lastname: Suiter
keywords: Disability evaluation; Surveys and questionnaire; Whiplash injuries