Validity and test-retest reliability of a disability questionnaire for essential tremor

BACKGROUND: One important outcome in clinical trials is patients' own opini ons about whether the medication alleviates their symptoms and improves the ir ability to function. A valid and reliable method with which to assess th is subjective information is important. OBJECTIVE: To determine the validity and test-retest reliability of the Col umbia University Disability Questionnaire for Essential Tremor (ET). METHODS: Patients with ET underwent a 2.5-hour evaluation, including a 36-i tem tremor disability questionnaire, to assess the functional impact of tre mor, a 26-item videotaped tremor examination rated by a neurologist, a 15-i tem performance-based test, and quantitative computerized tremor analysis. We determined the validity and test-retest reliability of the tremor disabi lity questionnaire. Correlations between variables were assessed using Pear son's correlation coefficients and test-retest reliability with the weighte d kappa statistic. RESULTS: Ninety-five patients with ET participated. The score on tremor dis ability 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 analysi s results were less robust, but each remained significant, including mean a mplitude of dominant arm tremor while arms were extended (r = 0.56, p <0.00 1), while drawing a spiral (r = 0.42, p = 0.01), and while pouring (r = 0.3 4, 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, i ncluding a neurologist's clinical ratings, a performance-based test of func tion, and quantitative computerized tremor analysis results. The questionna ire would be useful in clinical trials in which it could be used as a relia ble and valid tool to assess disability in ET.