Minimal Detectable Change of Experienced and Novice Listeners' Ratings of Overall Severity of Voice Quality in Adductor Laryngeal Dystonia.

PURPOSE: This study determined the minimal detectable change (MDC) scores for experienced and novice listeners' ratings of overall severity of voice quality for speakers with adductor laryngeal dystonia (ADLD) and typical controls. We also determined MDCs as a function of speaker severity and listener experience.

METHOD: Ten experienced listeners (ELs) and 12 novice listeners (NLs) rated overall severity of voice quality in 39 speakers with ADLD and 10 controls using a 100-mm visual analog scale across two rating sessions. MDCs at the 95% confidence level (MDC95) were calculated for all speakers. MDC95 scores also were calculated as a function of speaker group, perceived speaker severity using averaged EL ratings as the reference standard (grouped as typical, mild, moderate, severe), and listener experience group.

RESULTS

The MDC95 for EL ratings of overall severity of voice quality for all speakers was 11.10 mm; for NLs, the MDC95 was 8.73 mm. As a function of speaker group, the MDC95 for EL ratings was 12.31 mm for speakers with ADLD (n = 39) and 0.89 mm for controls (n = 10). For NLs, the MDC95 was 9.32 mm for speakers with ADLD and 4.72 mm for controls. As a function of speaker severity (n = 13 typical, n = 9 mild, n = 12 moderate, n = 15 severe), MDC95 scores ranged from 4.22 to 13.77 mm for ELs, whereas MDC95 scores ranged from 4.95 mm to 12.25 mm for NLs. Across both listener groups, mildly and moderately dysphonic speakers required larger MDC95 scores compared to speakers without dysphonia for such differences to be considered beyond measurement error. Differences in MDC95 scores ranged from 1 to 4 mm between listener groups across speaker severities.

CONCLUSION

Results have implications for measuring and interpreting auditory-perceptual outcomes for speakers with ADLD with different voice quality severities when they are evaluated by ELs and NLs in clinical and research contexts.