In order to determine the physiological responses associated with sound exposures or the physiological costs the human hearing has to pay for noise, a comprehensive, reliable method was developed which uses pure-tone audiometry to measure and analyze via regression analysis hearing threshold shifts and their restitution. In audiometry, how loud a sound can be perceived – especially with high measurement frequencies in excess of 4 kHz – depends greatly on the positioning of the headphones over the ear canal. Minor deviations of the headphones from the optimal position already lead to changes in the level of several decibels. Thus, precise measurement of threshold shifts and their restitution requires exact and repeatable positioning over the ear canal. To that end, the test subjects are offered a high-frequency 6-kHz tone approximately 30 dB above their individual hearing threshold. They were instructed to place the headphones over the ear canal in such a manner that they could subjectively hear the tone the loudest. Before each test series, the test subjects' initial hearing threshold has to be determined at several frequency measuring points. During the actual tests, the frequency of the maximum threshold shift is determined within 2 minutes after the end of the exposure (TTS₂). At the frequency of the maximum threshold shift, the remaining threshold shift has to be measured at reasonably spaced time intervals until the initial hearing threshold shift is reached again (i.e., the time t(0 dB)). The so-obtained real values TTS_{2 real} and t(0 dB)_real as isolated measurement values are not sufficient, however, to make well-founded statements about the entirety of audiometric data. Since the restitution of hearing threshold shifts is approximately log-linear with respect to time, the measurement values can be analyzed statistically using linear regression techniques. The determination of the values TTS₂, t(0 dB), and the regression function TTS(t) which are obtained from the regression analysis makes it possible to determine an integral value which as the area under the function TTS(t) allows statements about the risk to the hearing. In order to achieve correct results, the point in time when the initial hearing threshold is reached once again needs to be weighted. The characteristic value IRTTS (Integrated Restitution Temporary Threshold Shift) shows the physiological costs of sound exposures as a numeric value (measured in dBmin). If it is related to reference values for permissible sound exposures of 85 dB(A) / 8 h or 94 dB(A) / 1 h, it can express the relative risk of the studied sound exposures (the so-called risk factor). The real characteristic values of the measurements as well as the regression results have to be tested for statistical significance. Since measurements of the restitution of hearing threshold shifts in principle do not exhibit a normal distribution, a non-parametric test, e.g., the WILCOXON test, has to be applied.