| Congenital impairment | Hearing impairment considered to be present and detectable at or very early after birth, including those babies with an early or perinatally acquired impairment. This was the default classification when there was no indication that the impairment was either acquired or late onset |
| Acquired impairment | Hearing impairment that first manifested itself postnatally and could be attributed to an identifiable exogenous cause |
| Late onset impairment | Hearing impairment that first manifested itself postnatally but could not be attributed to an identifiable exogenous cause |
| Progressive impairment | Hearing impairment that may be congenital, acquired or late onset but which worsened over time |
| Confirmation of impairment | The process of establishing the presence of hearing impairment by an age-appropriate threshold test with high reliability of the results |
| Confirmation with audiological certainty | Confirming the presence of hearing impairment by age-appropriate tests where both the degree and type of impairment were established |
| Referral | The process of referring a child to an audiologist for an assessment of hearing threshold either reactively because of professional or parental concern or from a hearing screen. When used as an indicator of outcome only referrals resulting in confirmation were included |