Evolution of Hearing Thresholds and the Effect of Age

Hearing loss is known to be a worldwide common problem caused by noise, aging, disease, and heredity. The aim of this study was to investigate how hearing thresholds evolve over time and how this evolution depends on age. Hearing thresholds were measured on 226 subjects the at different time-points and were categorized into normal (< 25 dB), mild (25 - 40 dB), moderate (41 - 65 dB) and severe ( 66 dB). A marginal model using Generalized Estimating Equations (GEE) and a generalized linear mixed model (GLMM) were fitted to the data. From both models it was observed that older subjects tend to have more hearing loss. In addition, from GLMM, it was noticed that the rate of decrease in hearing ability is larger for an older subject. This shows that the evolution of hearing loss depend on age at entry into the study. Empirical Bayes estimates were considered in GLMM to make inference about the random effects. It can be concluded that age has an effect on hearing thresholds and on their evolution over time.