Re: Does hearing ability decrease dramatically between 5 and 20 years of age?

Hearing sensitivity does decrease with age in most industrialized 
societies, including New Zealand.  The range of frequencies 
gradually reduces as we get older.  The first measurable change 
occurs in the population at around age 55 years on average and 
gradually decreases from then on.  There also is a gender difference 
of about 20 years – that is, the hearing sensitivity of the typical 60 year 
old male is similar to the 80 year old female.

Age-related changes in hearing occur only in typical, western 
industrialized societies.  In central Africa and on the Easter Islands in 
the South Pacific where individuals are very healthy and have very 
good diets and are not exposed to the excess noise of "modern" 
society, hearing sensitivity does not change with age.  Individuals in 
these societies who are 90 years old have hearing sensitivity just like 
20 year olds.  It is probably not aging that causes hearing decline but 
rather other factors such as diet and noise exposure.

So, the age range for your study, 5 to 20 years, will work well.  
However, because people in this age range can have hearing loss 
for a variety of other factors such as infections, genetics, exposure to 
excess noise, etc., it would be useful to determine that they do not 
have any existing hearing problem.  Simply develop a short 
questionnaire and ask them if they believe that their hearing is 
normal in each ear, if they have a history of hearing loss in their 
immediate family (except for the elderly members), if they have a 
history of ear infections, exposure to excessively loud sounds for long 
periods, etc.  Selecting subjects based on their age and the answers 
to the questions will go a long way to determining that their hearing is 
normal.