Hager 1982.

Methods	CBA study
Participants	Various workers n = 43 USA 1 company
Interventions	Intervention: hearing protection as part of HLPP in company; n = 27 Control: non‐exposed colleagues; n = 16
Outcomes	Hearing thresholds at entrance minus HT at follow‐up at 0.5, 1, 2, 3, 4, 6 kHz Follow‐up average 5 and 10 years
Notes	Long‐term Comparability ‐ intervention/control: age: ? hearing: intervention 8.1 dB 4 kHz; control 0.3 dB 4 kHz
Risk of bias
Bias	Authors' judgement	Support for judgement
14. Blinding (subjects)	High risk	no blinding
15. Blinding (outcome assessors)	High risk	no blinding
16. Retrospective unplanned subgroup analyses	Low risk	no additional analyses
17. Follow‐up	Low risk	same time (5years)
18. Statistical tests	Low risk	t‐test
19. Compliance	Unclear risk	not reported
20. Outcome measures	Unclear risk	audiometry quality not reported
21. Selection bias (population)	Low risk	same factory
22. Selection bias (time)	Unclear risk	control subjects not grouped according to period of time
23. Randomization	High risk	not randomised
24. Allocation concealment	Unclear risk	not randomised, not applicable
25. Adjustment for confounding	Unclear risk	age corrected control group
26. Incomplete outcome data	Low risk	not reported