Background: Poor voice quality due to a voice disorder can lead to a reduced quality of life. In occupations where voice use is substantial it can lead to periods of absence from work.
Objectives: To evaluate the effectiveness of interventions to prevent voice disorders in adults.
Search strategy: We searched MEDLINE (PubMed, 1950 to 2006), EMBASE (1974 to 2006), CENTRAL (The Cochrane Library, Issue 2 2006), CINAHL (1983 to 2006), PsychINFO (1967 to 2006), Science Citation Index (1986 to 2006) and the Occupational Health databases OSH-ROM (to 2006). The date of the last search was 05/04/06.
Selection criteria: Randomised controlled clinical trials (RCTs) of interventions evaluating the effectiveness of treatments to prevent voice disorders in adults. For work-directed interventions interrupted time series and prospective cohort studies were also eligible.
Data collection and analysis: Two authors independently extracted data and assessed trial quality. Meta-analysis was performed where appropriate.
Main results: We identified two randomised controlled trials including a total of 53 participants in intervention groups and 43 controls. One study was conducted with teachers and the other with student teachers. Both trials were poor quality. Interventions were grouped into 1) direct voice training, 2) indirect voice training and 3) direct and indirect voice training combined.1) Direct voice training: One study did not find a significant decrease of the Voice Handicap Index for direct voice training compared to no intervention.2) Indirect voice training: One study did not find a significant decrease of the Voice Handicap Index for indirect voice training when compared to no intervention.3) Direct and indirect voice training combined: One study did not find a decrease of the Voice Handicap Index for direct and indirect voice training combined when compared to no intervention. The same study did however find an improvement in maximum phonation time (Mean Difference -3.18 sec; 95 % CI -4.43 to -1.93) for direct and indirect voice training combined when compared to no intervention. 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.
Authors' conclusions: We found no evidence that either direct or indirect voice training or the two combined are effective in improving self-reported vocal functioning when compared to no intervention. The current practice of giving training to at-risk populations for preventing the development of voice disorders is therefore not supported by definitive evidence of effectiveness. Larger and methodologically better trials are needed with outcome measures that better reflect the aims of interventions.