The reliability and sensitivity to change of acoustic measures of voice quality.

This study aimed to evaluate the reliability and sensitivity to change of three commonly used acoustic parameters as measured by the Multi-Dimensional Voice Programme (MDVP); jitter, shimmer and noise-to-harmonic ratio. A total of 231 subjects' voices were recorded and analysed. The sample comprised 145 dysphonic patients who received intervention (surgery or voice therapy), 36 dysphonic patients who received no intervention, and 50 non-dysphonic (normal) subjects. All voices were recorded and analysed on two occasions (before and after treatment, or test-retest assessment) using a standard procedure. These data were analysed using standard psychometric procedures for assessing reliability and responsiveness. The acoustic analysis measures demonstrated poor to moderate reliability and effect size with respect to their sensitivity to change. Caution should be exercised in the injudicious use of computer-based acoustic analysis systems as an isolated measure of voice outcome in any clinical trial of interventions aimed at improving voice quality.