Lee‐Feldstein 1993.

Methods	CBA study
Participants	Automobile workers n = 11,435 USA 1 company
Interventions	Intervention: HLPP; n = 11,104, after cluster adjustment n = 97 Control: non‐exposed colleagues; n = 331
Outcomes	Rate of STS, average change in mean hearing threshold at 2, 3 and 4 kHz in the worst ear follow‐up average 5 years
Notes	Long‐term Comparability ‐ intervention/control: age: adjusted hearing: adjusted
Risk of bias
Bias	Authors' judgement	Support for judgement
14. Blinding (subjects)	High risk	not blinded
15. Blinding (outcome assessors)	High risk	not blinded
16. Retrospective unplanned subgroup analyses	Low risk	no additional analyses
17. Follow‐up	Low risk	similar
18. Statistical tests	Unclear risk	not reported
19. Compliance	Unclear risk	not reported
20. Outcome measures	Low risk	audiometry quality reported
21. Selection bias (population)	Low risk	same factory
22. Selection bias (time)	Low risk	same period
23. Randomization	High risk	not randomised
24. Allocation concealment	Unclear risk	not randomised, not applicable
25. Adjustment for confounding	Low risk	adjusted for age and hearing loss
26. Incomplete outcome data	Unclear risk	not reported