The most relevant earlier study was conducted in a defined geographical region of England (Trent, population 4.7 million) in 1995². Comparing children born in the same cohorts showed significant difference between the two studies whereas children of the same age showed no significant difference in prevalence indicating that prevalence has not decreased with time but that age is the main determinant of prevalence.

2. Fortnum H, Davis A. Epidemiology of permanent childhood hearing impairment in Trent Region, 1985-1993. Brit J Audiol 1997;31:409-446

3. Fortnum H M, Summerfield A Q, Marshall D H, Davis A C, Bamford J M. Prevalence of permanent childhood hearing impairment in the United Kingdom and implications for universal neonatal hearing screening: questionnaire-based ascertainment study. Brit Med J 2001;323:536-539