Figures for the UK suggest that 70 in every 1,000 people have "some" hearing loss, eight in every 1,000 have severe hearing loss, and one in every thousand have prelingual, total deafness.
This figure will change, as definitions of deafness change, with use of hearing aids, etc.
We can divide the population in different ways and look at deafness in these groups
Many more older people have hearing loss than younger people. The proportion of people with hearing loss will increase in Europe and America, as the proportion of older people increase. For example, in 1987, the population of people over 65 in the USA was 11.6%. In 2000, it will be 13%, which is an increase of 12%, so we can expect a corresponding increase in deafness.
More men are deaf than women. This is mainly because men have traditionally worked in the heavy industries. But boys are also more susceptible to deafness in childhood, too.
This is a tricky one, because in many demographic studies, it has been hard to weed out "race" from "wealth", because in countries with mixed populations, the white people tend to be the richest race.
Still, deafness in white people in the USA outnumbers that of black people, 2:1. This is probably because
i) genes for deafness are more common in white people
ii) "non-white" tends to equal "non-wealthy", so poor people might die of an illness that a richer person would survive but be left deaf.
iii) under-reporting. The data are only as good as the collection. We can't be sure that the counts are accurate. It is well-known that ABC1s in the UK are far more likely to come and have their hearing checked than C2DEs.
This question of data-collection is very important. Recently some American linguists have been doing some research on the sign language used in Nicaragua. They went from village to village asking if anyone there was deaf, and people always said "no". They were close to being forced to conclude that nobody in the country was deaf (which they knew was not true) when they accidentally asked if there was anyone in the village who did not speak. This was the solution to the problem and after that they found plenty of deaf people. This mistake can be understood when we think that the villagers can't see if someone can hear or not (because none of us can perceive something on another person's behalf), but they can see if the person is not speaking. There were also times when the researchers stayed in a village for several days and were only told about a deaf person in the village as they were leaving. We can understand this reticence, too. If you do not know a stranger's motives for asking about deafness, you might assume that they were going to harm the deaf person. This distrust of strangers' motives might also explain low statistics for deaf people in censuses among generally less powerful communities who are often treated with less respect by the authorities. It might also explain why there are few cases of hereditary deafness because a deaf mother might fear losing her deaf baby if the authorities find out.
However, assuming that data collected is trustworthy to some extent, one important point to come from this is the effect that hereditary deafness can have on deaf communities. White people in the UK are more likely to come from deaf families, and so be a central part of the deaf community. Black and Asian deaf people in the UK very rarely have deaf parents, so are more peripheral in the deaf community. The study of sign language in Nicaragua planned to look at the language of deaf people from deaf families, to compare it with that of those from hearing families. When they couldn't find a single deaf family (except, at last, one where there was deaf aunt and niece) they realised that this was going to have very important ramifications for the deaf community there. This means that Nicaraguan deaf have a very different type of community from British deaf and can expect different patterns of language.
d) Other factors
i) Geography - communities cut off from other people may have high incidences of deafness if there is a gene for deafness in the community. There are a few recorded such communities, including Martha's Vineyard of the 18th and 19th centuries (see Nora Groce's book), and present day Mexico in the Yucatan peninsula, and Grand Cayman in the West Indies, some Bedouins in Israel and some people in Bali in Indonesia.
The effect of consanguinity can also be seen among Asians from the Indian subcontinent in Britain today. There is a high incidence of deafness here, because the community is culturally cut off from the wider gene pool, even if not physically.
ii) War - this causes deafness in large numbers. In the past, war mainly caused deafness in hearing young men who were soldiers (which meant, again, there were more deaf men than women). Now, with so many civilians being caught up, there are many more children, and people of all types, who are deaf as a result of war. This has massive consequences, that we can only begin to consider. Deaf people in (for example) the Lebanon, Uganda and Angola have to develop their own communities, with no history and no support from previous generations, and all in devastated countries. In these cases we can't expect their languages and communities or attitudes to deafness to be like the British ones.
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