Simpson 1994.
| Methods | CBA study | |
| Participants | Various occupations in 21 companies n = 13283 USA | |
| Interventions | Intervention: well‐implemented HLPP Control: poor quality HLPP | |
| Outcomes | Rate of STS defined as on average ≥ 10 dB at 2, 3 and 4 kHz in either ear Follow‐up average 1 year | |
| Notes | Long‐term Comparability ‐ intervention/control: age: ? hearing: ? |
|
| 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 period (second audiogram fell within time window of 6‐18 months) |
| 18. Statistical tests | Unclear risk | no tests mentioned |
| 19. Compliance | Unclear risk | not reported |
| 20. Outcome measures | Unclear risk | audiometry quality not reported |
| 21. Selection bias (population) | High risk | different companies |
| 22. Selection bias (time) | Unclear risk | not reported |
| 23. Randomization | High risk | not randomised |
| 24. Allocation concealment | Unclear risk | not randomised, not applicable |
| 25. Adjustment for confounding | Unclear risk | not reported |
| 26. Incomplete outcome data | Unclear risk | not reported |
ANOVA = analysis of variance ANSI = American National Standards Institute CBA = controlled before and after (study) CI = confidence interval ? = no information available HL = hearing loss HLPP = hearing loss protection programme HPD = hearing protection device HR = hazard ratio HT = hearing threshold ITS = interrupted time series L = left Leq = equivalent continuous sound level MANOVA = multivariate analysis of variance md = median NIHL = noise‐induced hearing loss NLI = Noise level indicator PEL = permissible exposure level R = right REAT = real ear attenuation at threshold RR = risk ratio STS = standard threshold shift TTS = temporary threshold shift TWA = time‐weighted average