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.
To determine the validity and test–retest reliability of the Columbia University Disability Questionnaire for Essential Tremor (ET).
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 video- taped 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.
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).
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.