title: Validity and test-retest reliability of a disability questionnaire for essential tremor.
abstract: BACKGROUND
  One important outcome in clinical trials is patients' own opinions about whether the medication alleviates their symptoms and improves their ability to function. A valid and reliable method with which to assess this subjective information is important.
  
  
  OBJECTIVE
  To determine the validity and test-retest reliability of the Columbia University Disability Questionnaire for Essential Tremor (ET).
  
  
  METHODS
  Patients with ET underwent a 2.5-hour evaluation, including a 36-item tremor disability questionnaire, to assess the functional impact of tremor, a 26-item videotaped tremor examination rated by a neurologist, a 15-item performance-based test, and quantitative computerized tremor analysis. We determined the validity and test-retest reliability of the tremor disability questionnaire. Correlations between variables were assessed using Pearson's correlation coefficients and test-retest reliability with the weighted kappa statistic.
  
  
  RESULTS
  Ninety-five patients with ET participated. The score on tremor disability questionnaire correlated with the neurologist's clinical ratings (r = 0.57, p <0.001) and the total score on the performance-based test (r = 0.69, p < 0.001). Correlations with quantitative computerized tremor analysis results were less robust, but each remained significant, including mean amplitude of dominant arm tremor while arms were extended (r = 0.56, p <0.001), while drawing a spiral (r = 0.42, p = 0.01), and while pouring (r = 0.34, p = 0.04). The questionnaire was readministered to 32 subjects, and the test-retest reliability was substantial (weighted kappa = 0.67).
  
  
  CONCLUSIONS
  This Tremor Disability Questionnaire demonstrated substantial reliability, and it correlated with multiple measures of tremor severity, including a neurologist's clinical ratings, a performance-based test of function, and quantitative computerized tremor analysis results. The questionnaire would be useful in clinical trials in which it could be used as a reliable and valid tool to assess disability in ET.
authors.affiliation: The Gertrude H. Sergievsky Center, Department of Neurology, College of Physicians and Surgeons, Columbia University, New York, NY, USA.
authors.forename: E D
authors.initials: ED
authors.lastname: Louis
authors.forename: L F
authors.initials: LF
authors.lastname: Barnes
authors.forename: K J
authors.initials: KJ
authors.lastname: Wendt
authors.forename: S M
authors.initials: SM
authors.lastname: Albert
authors.forename: S L
authors.initials: SL
authors.lastname: Pullman
authors.forename: Q
authors.initials: Q
authors.lastname: Yu
authors.forename: F R
authors.initials: FR
authors.lastname: Schneier
mesh_terms: D000203:Activities of Daily Living / Q000145:classification; D000368:Aged; D000369:Aged, 80 and over; D004185:Disability Evaluation; D020329:Essential Tremor / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009048:Motor Skills; D015203:Reproducibility of Results