Applicability of function-based analysis in retrospective data analysis of noise-induced hearing loss in the Finnish Defence Forces

In retrospective studies, analysis of statistical cross-sectional and longitudinal data is always a challenge. To obtain statistically reliable results, the quantity and quality of the data have to be carefully evaluated. In this study, application of specific functions that establish versatile evaluation of retrospective data in the time domain was studied in a case of retrospective analysis of noise-induced hearing loss (NIHL) among 1337 soldiers in the Finnish Defence Forces (FDF). The data included a number of audiogram (AG) variables that were recorded from subjects at varying intervals. Specific functions were used to present AG results according to one common continuous time scale, the age of the subjects. The aim of this study was to evaluate how much inaccuracy this kind of presentation would produce in analysis of the AG results. The inaccuracy was evaluated by comparing the median values of function-based values and the original data values according to the age of the subjects. The results of the study showed that the resulting error was less than 3 dB between the ages of 24–48 for all the AG variables for all the subjects in this data. This level of error is significantly less than the typical measurement resolution (5 dB) of AG, indicating that the proposed function-based analysis is appropriate for analysis of NIHL data.