Meta-analysis of typical cohort studies on NIHL incidence
| Author | Type of factory | Population | Study duration | Years of follow-up | Noise level (max or mean)(dB(A)) | NIHL incidence (%) | |||
| N | Exposure duration (years) | HFNIHL | SFNIHL | Average | |||||
| Jing59 | Oil field | 673 | 1.0–30.0 | 2006–2010 | 5 | 106.8 | 30.6 | 3.7 | 17.2 |
| Xu60 | Electrolytic aluminium | 1929 | 1.0–30.0 | 2008–2012 | 5 | 87.1±2.2 | 16.6 | 10.9 | 13.8 |
| He61 | Automobile | 397 | 8.8±8.7 | 2014–2016 | 3 | 101.3 | 34.3 | 2.3 | 18.3 |
| Total | – | 2999 | 8.8±8.7 | 2006–2016 | – | 98.4±7.2 | 22.1 | 8.1 | 15.1 |
dB(A), A-weighted decibels; HFNIHL, high-frequency noise-induced hearing loss; NIHL, noise-induced hearing loss; SFNIHL, speech-frequency noise-induced hearing loss.