A Cochrane review [Abstract] 1 included 6 studies with a total of 262 subjects. Four studies were conducted with primary school or kindergarten teachers, one with student teachers and one with telemarketers. Interventions were grouped into 1) direct voice training, 2) indirect voice training and 3) direct and indirect voice training combined. Three studies found similar self-reported vocal symptoms between those who attended direct voice training and those who were in a no intervention control group (SMD 0.27, 95% CI -0.12 to 0.66). Two studies found similar self-reported vocal symptoms between those who attended indirect voice training and those who were in a no intervention control group (SMD 0.44, 95% CI -0.03 to 0.92). One study found similar scores on the Voice Handicap Index for those who had direct and indirect voice training combined and for those who had no intervention. Two studies compared a combination of direct and indirect voice training with indirect voice training only. Both studies found similar scores for self-reported phonation difficulty (MD -5.55, 95% CI -23.75 to 12.66) in both groups.
No work-directed studies were found. None of the studies found evaluated the effectiveness of prevention in terms of sick leave or number of diagnosed voice disorders.
Comment: The quality of evidence is downgraded by study quality (inadequate or unclear allocation concealment) and by imprecise results (limited study size for each comparison).
Primary/Secondary Keywords