A Cochrane review [Abstract] 1 included 3 studies with a total of 63 subjects. Data were available from 41 participants in two trials. The loudness of patients' voices were increased by between 7-18%, depending on the speaking task being performed. After six months the degree of improvement was reduced but was still statistically significant. The clinical significance of these improvements is less clear.
Another Cochrane review [Abstract] 2 included 6 trials with a total of 159 patients. A statistically significant result was only reported for the diagnostic rhyme test used in the study of Lee Silverman Voice Treatment -LOUD (LSVT-LOUD) versus a modified version of this therapy (LSVT-ARTIC). In this case a difference of 12.5 points (95%CI -22.2 to -2.8) between the mean changes in favour of the LSVT-LOUD group was reported for a speech sample overlaid with Babble noise; this difference was not reproduced for the two additional noise conditions under which the speech samples were assessed. LSVT-LOUD also outperformed LSVT-ARTIC and Respiration therapy (RT) in improving loudness, with a difference in reading a sample text of 5.0 dB (95%CI -8.3 to -1.7) and 5.5 dB (95% CI 3.4 to 7.7) respectively, and a difference in monologue speech of 2.9 dB (95% CI 0.6 to 5.2) versus RT.
Comment: The quality of evidence is downgraded by imprecise results (few patients and wide confidence intervals) and inconsistency (heterogeneity in interventions and outcomes).
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