Muhr 2016.

Methods	CBA study
Participants	Army conscripts (n= 1234) Control group: before military service in 2002‐2004 (n = 839), Intervention group: in military service 2004‐2005 (n = 395), 40 servicemen from the armoured regiment included in the control‐group are also included in the intervention group. Mean age: intervention, 19 years, control, 18 years at enrolment Gender: male Hearing ability: most participants had maximum hearing thresholds of 25 dB for frequencies 0.5 to 8 kHz in both ears at enrolment to study (I 88.4%, C 85.5%) Exposure: intervention group exposed to impulse noise from shooting Sweden Military
Interventions	Intervention: HLPP including HPDs and administrative controls (n = 395) Control: non‐exposed to military noise, waiting for training period (n = 839)
Outcomes	STS ≥ 15 dB at 1 or both ears at any of 0.25, 0.5, 1, 2, 3, 4, 6 or 8 kHz between baseline and follow‐up, hearing test with average follow‐up of 8 months (intervention group) and 13 months (control group)
Notes
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 subgroup analysis, data dredging unlikely
17. Follow‐up	Unclear risk	approximate difference of 5 months in follow‐up between intervention and control, 1.5 times longer for control
18. Statistical tests	Low risk	RR (95%CI)
19. Compliance	Unclear risk	not reported
20. Outcome measures	Low risk	audiometry quality reported
21. Selection bias (population)	Low risk	all subjects recruits to the army
22. Selection bias (time)	High risk	different time periods, 2004/2005 vs 2002‐2004
23. Randomization	High risk	no randomisation
24. Allocation concealment	High risk	no randomisation
25. Adjustment for confounding	Low risk	Control and intervention groups of similar age and hearing, baseline for other confounders not reported
26. Incomplete outcome data	Unclear risk	loss of follow‐up not reported