The effect of ageing on hearing thresholds Increasing age had a significantly deleterious effect on hearing thresholds (Figure 3). The univariate ANOVA revealed that significant deterioration of pilots’ hearing threshold hadoccurred already at the age of 30 years in relation to measurements at recruitment but only at 4 kHz (Table 2). It is important to note that thresholds at 0.5 kHz ‘improved’ with ageing, an observation that can be explained by inadequate ambient noise control at the time the recruitment audiogram was performed.