Research Progress and Suggestions on the Noise Equal Energy Hypothesis: A Systematic Review and Meta-analysis

This study aims to evaluate the applicability and limitations of the equal energy hypothesis (EEH) in assessing noise-induced hearing loss (NIHL) and investigate the role of the kurtosis parameter (reflecting noise temporal structure) in assessing NIHL, providing a basis for refining EEH theory.

A systematic review and meta-analysis were conducted to summarize studies related to EEH, systematically collecting its development, validation, and revision suggestions. The weighted mean difference (WMD) and odds ratio (OR) of hearing loss caused by different types of noise were used to evaluate the role of noise kurtosis in the evaluation of NIHL.

A total of 57 articles were included, containing experimental and cross-sectional studies. Evidence showed significant limitations in the EEH when assessing non-steady noise, leading to an underestimation of NIHL under equal energy conditions. Animal experiments verified a critical level for assessing NIHL when using the EEH, with ranges of 90-135 dB in chinchillas and 108-120 dB in guinea pigs. EEH could be revised in the frequency domain (spectrum) and time domain (e.g., kurtosis). Meta-analysis showed that in animal experiments, WMD for permanent threshold shifts (PTSs) at 2, 4, and 8 kHz (PTS at 2, 4, and 8 kHz) was 3.30 dB (95% confidence interval [95% CI]: 2.22-4.37); in population surveys, OR for high-frequency NIHL was 1.78 (95% CI: 1.36-2.32). Logistic regression analysis confirmed kurtosis as a risk factor for NIHL (P < 0.001). Kurtosis adjustment for cumulative noise exposure and equivalent sound level adequately improved the accuracy of hearing loss estimation.

The EEH's limitations in assessing NIHL caused by non-steady noise can be remedied by adjusting noise energy metrics using kurtosis. Our findings suggest that EEH could be revised as an "equal energy and equal kurtosis hypothesis."