Minimal Detectable Change of Experienced and Novice Listeners' Ratings of Overall Severity of Voice Quality

The primary purpose of this study was to determine the minimal detectable change (MDC) scores-defined as the smallest amount of change greater than measurement error-for experienced and novice listeners' ratings of overall severity of voice quality for speakers with and without voice disorders. A secondary purpose was to determine the MDC scores as a function of speaker severity and listener experience.

Ten experienced listeners (ELs) and 10 novice listeners (NLs) rated overall severity of voice quality in 41 speakers with voice disorders and nine without voice disorders using a 100-mm visual analog scale across two rating sessions. MDCs at the 95% confidence level (MDC₉₅) were calculated. MDC₉₅ scores also were calculated as a function of perceived speaker severity using averaged EL ratings from session one as the reference standard (categorized as typical, mild, moderate, and severe) for each listener group.

The MDC₉₅ for EL ratings of overall severity of voice quality for all speakers was 8.83 mm; for NLs, the MDC₉₅ was 9.33 mm. As a function of speaker severity (n = 11 typical, n = 11 mild, n = 13 moderate, and n = 15 severe), MDC₉₅ scores ranged from 3.70 to 15.18 mm for ELs and from 4.72 to 12.13 mm for NLs. For NLs, mildly dysphonic speakers required the largest MDC₉₅ scores to be considered beyond measurement error. For ELs, MDC₉₅ scores were largest for moderately dysphonic speakers.

Results have implications for measuring and interpreting auditory-perceptual outcomes for speakers with voice disorders when they are evaluated by experienced and novice listeners in both clinical and research contexts.