Ilomäki 2008.

Methods	RCT
Participants	59 female primary school teachers in Finland Mean age: 41.5 in the VHL group (control) and 42.2 in the VT group (intervention) Experience in years, mean: 15.8 in the VHL group (control) and 15.6 in the VT group (intervention) Vocal demands, mean: 23 teaching hours per week in the VHL group (control) and 24 hours in the VT group (intervention) Total hours taught during the autumn term: 420 in the VHL group and 439 in the VT group Class size: mean of 19 pupils in the VHL group and 20 in the VT group Differences between groups were non‐significant
Interventions	1) Indirect voice training (voice hygiene lecture only) (29) After the first pre‐intervention recordings, all teachers attended a theoretical voice hygiene lecture lasting 3 hours. The course objectives of the lecture were to gain knowledge and awareness of the basics of voice and speech production, the main factors causing vocal loading in teachers, methods available to avoid overloading, and basics of economic versus non‐economic voice use 2) Direct and indirect voice training (voice training and voice hygiene lecture) (30) This group exercised their voices in 5 voice training lessons (each lesson 1 hour plus individualised homework) during 9 weeks. The course objectives of the voice training course were to gain ease and endurance in voice production, and getting rid of any poor vocal habits. The learning methods were introspections, discussions, voice exercises and individualised homework with a view to finding economic voice production, i.e. avoidance of excessive muscle tension of the larynx, deep breathing technique, firmness of phonation without effort, well‐resonating voice quality to improve audibility, and adequate individual pitch and loudness range and variation.
Outcomes	1) Phonation difficulty, voice quality, throat tiredness 2) Voice quality, firmness of phonation, fundamental frequency (F0), sound pressure level, alpha ratio (the ratio between the spectral energy below and above 1000 Hz), jitter, shimmer
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	Unclear risk	"All 60 teachers attended a voice hygiene lecture at the beginning of term; 30 of them were randomly assigned to a voice training group" (p. 85). No further details reported about the method of randomisation.
Allocation concealment?	Unclear risk	No details reported regarding whether allocation was concealed or not
Blinding? All outcomes	Unclear risk	"Three experienced voice trainers evaluated the text samples for voice quality and firmness of phonation..." (p. 86). The authors do not report if the evaluators were blinded to the experimental conditions to which the participants had been assigned.
Incomplete outcome data addressed? All outcomes	High risk	"One of the teachers in the VHL group was excluded from the study at the end of the term because of incomplete recordings" (p. 85). However, in the raw data provided by the authors, three participants had dropped out of the experimental group and the control group somehow remained the same.
Free of selective reporting?	Low risk	The authors report results for each of the outcomes listed in the Methods section