Figure 2: The prevalence of hearing impairment

as a function of age group (18-40, 41-60 and 61-80)
as a function of degree of hearing impairment (25, 35 and 45 dB HL+)
and as a function of noise exposure (<80, 80-89 and 90-99 dB(A) Lequ 40 for 50 years equivalent) that was gained through occupational noise exposure for average hearing level (0.5, 1, 2 and 4 kHz) and for 4 kHz alone.

Data taken from Davis 1995 and presented in these figures especially to draw out main points for this work.

Source: SCENIHR,  Potential health risks of exposure to noise from personal music players and mobile phones including a music playing function (2008) , Section 3.5.3., Page 29.