Optimising outcome assessment of voice interventions, II: Sensitivity to change of self-reported and observer-rated measures.

OBJECTIVES: A wide range of well validated instruments is now available to assess voice quality and voice-related quality of life, but comparative studies of the responsiveness to change of these measures are lacking. The aim of this study was to assess the responsiveness to change of a range of different measures, following voice therapy and surgery.

DESIGN: Longitudinal, cohort comparison study.

SETTING: Two UK voice clinics.

PARTICIPANTS: One hundred and forty-four patients referred for treatment of benign voice disorders, 90 undergoing voice therapy and 54 undergoing laryngeal microsurgery.

MAIN OUTCOME MEASURES: Three measures of self-reported voice quality (the vocal performance questionnaire, the voice handicap index and the voice symptom scale), plus the short form 36 (SF 36) general health status measure and the hospital anxiety and depression score. Perceptual, observer-rated analysis of voice quality was performed using the grade-roughness-breathiness-asthenia-strain scale. We compared the effect sizes (i.e. responsiveness to change) of the principal subscales of all measures before and after voice therapy or phonosurgery.

RESULTS: All three self-reported voice measures had large effect sizes following either voice therapy or surgery. Outcomes were similar in both treatment groups. The effect sizes for the observer-rated grade-roughness-breathiness-asthenia-strain scale scores were smaller, although still moderate. The roughness subscale in particular showed little change after therapy or surgery. Only small effects were observed in general health and mood measures.

CONCLUSION: The results suggest that the use of a voice-specific questionnaire is essential for assessing the effectiveness of voice interventions. All three self-reported measures tested were capable of detecting change, and scores were highly correlated. On the basis of this evaluation of different measures' sensitivities to change, there is no strong evidence to favour either the vocal performance questionnaire, the voice handicap index or the voice symptom scale.