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. 2017 Jul 7;2017(7):CD006396. doi: 10.1002/14651858.CD006396.pub4

Moshammer 2015.

Methods CBA (arc sin transformed linear regression analysis of HPD use on NIHL)
Austria
Type of industry: steel factory
Participants Fitters and welders at a steel factory
Age mean 16.4 years, range 14‐19 years
Gender, hearing ability not reported
Average noise exposure: 90.8 dB(A) (range 85.4‐107.4 dB(A) over 13.3 years (range 2‐23 years)
n = 125
Interventions Use of hearing protection, self‐reported percentage of use, geometric mean of responses on questionnaire at 3 annual health examinations when hearing level was measured
Outcomes Noise‐induced hearing loss at 4 kHz, measured as hearing level at baseline adjusted for age minus hearing level at end of follow‐up adjusted for age (information from the study authors); also the average hearing loss at 2, 3 and 4 kHz was measured
Notes The study was set up to predict hearing loss based on TTS at start of the study. Participants were selected from a cohort of workers that started as apprentices at the firm between 1982 and 1989, who had at least 2 years of noise exposure and who worked at places that were noisy
Risk of bias
Bias Authors' judgement Support for judgement
14. Blinding (subjects) High risk No blinding; participants chose themselves about wearing or not wearing HPD
15. Blinding (outcome assessors) Unclear risk Not clear if audiometrists were aware of HPD use
16. Retrospective unplanned subgroup analyses High risk different data analysis and results because of comments on journal article
17. Follow‐up Low risk regression analysis includes adjustment for different time of follow‐up (noise years)
18. Statistical tests Low risk multivariate analysis
19. Compliance Unclear risk self‐reports of use of hearing protectors in noisy areas, unclear how valid
20. Outcome measures Low risk NIHL was calculated from thresholds measured with audiogram minus age related HL
21. Selection bias (population) Low risk same workplaces, type of work (closed cohort in 1 steel plant)
22. Selection bias (time) Low risk workers in I and C started between 1982‐1989
23. Randomization High risk no randomisation, participants chose themselves how often they used HPDs in noisy areas
24. Allocation concealment High risk no randomisation
25. Adjustment for confounding Low risk adjusted confounders
26. Incomplete outcome data High risk > 60% lost to follow‐up