Oliveira 2009.

Methods	RCT
Participants	43 telemarketers in Brazil Age: 18 to 55 Sex: intervention group 64% and control group 83% female
Interventions	1) Direct voice training (14) The intervention group received an 8‐week training programme, including vocal warming‐up and cool‐down, as well as tasks to expand the psychodynamic aspects of voice production. In order to promote vocal warm‐up, facilitating sounds, body movement techniques with sound production, overarticulation exercises, semi‐occluded vocal tract exercises (hand‐over‐mouth technique) and chant talk exercises were used in 8 30‐minute modules offered weekly. The facilitating sounds included humming sounds associated with chewing movements, fricatives and voice sounds associated with ascending musical scales (from C3 to C4) in staccato and legato. For cool‐down, voice sounds were also used, with descending musical scales (from G3 to C3), as well as the yawn‐sigh technique and laryngeal manipulation. 2) No intervention (29)
Outcomes	1) Vocal attrition symptoms, voice symptom score
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	Unclear risk	"A total of 100 telemarketers (83.3%) attended the lecture, of whom 92 (76.6%) consented to participate in the current study. Subjects were then randomly assigned to an intervention group (n = 44) and a control group (n = 48)" (p. 77)
Allocation concealment?	Unclear risk	No details reported regarding whether allocation was concealed or not
Blinding? All outcomes	High risk	This study used self‐reported outcomes only and therefore blinding is not an issue
Incomplete outcome data addressed? All outcomes	High risk	"Of the 44 telemarketers in the intervention group, 4 changed positions, were unavailable, 10 had over 25% absence and 12 did not show up. The intervention group was, therefore, comprised of 14 telemarketers. Of the 48 telemarketers in the control group, 39 attended the evaluations and 29 the re‐evaluations; this meant a loss of 19 telemarketers". (p. 78‐9). In other words, the intervention and control groups suffered losses of 68% and 40% respectively. No action was taken by the authors to address this in the results.
Free of selective reporting?	High risk	The authors reported the results the self‐reported outcome for males and females separately. This was not justified in advance.