Q: What is the biggest statistical mystery in the deaf and hard of hearing community of the United States (and the world)?
A: How many of us there are. No one really knows. There are some demographic statistics available, but they are either outdated or unreliable because some people may not wish to identify themselves as having a hearing loss, or the question forms may not ask directly if a person has a hearing loss. The estimated demographic figure has ranged from 22 million deaf and hard of hearing to as high as 36 million deaf and hard of hearing. Of these, only a few million are considered "deaf" and the remainder are hard of hearing. Further muddying statistics is the fact that some "deaf" people may actually be hard of hearing, and some "hard of hearing" people may actually be deaf. There are certainly enough of us with hearing losses that companies recognize the potential purchasing power of such a large segment of society.
Statistics are primarily maintained by two Federal agencies: The National Center for Health Statistics (NCHS) which is under the Centers for Disease Control (CDC), and the U.S. Census Bureau. According to the NCHS, as of 1994 4.5 million Americans - a small percentage of the total number with hearing loss - were using assistive technology to help them deal with hearing impairments. Of these, the most commonly used device is the hearing aid, and the least common "device" is an interpreter.
While most people with hearing loss are older folks who have lost hearing with age, approximately 12 out of every 1,000 persons with hearing impairment is under 18 years of age, based on the most recently available NCHS statistics. That means that the chances are excellent that at least one student in your child's school will have a hearing loss.
The Census Bureau offers demographical statistics on disability and employment, taken from a Survey of Income and Program Participation (participation in public assistance programs). That data has numbers only in the thousands, rather than the millions. One interesting pattern that emerges from this statistical data set is that people with less severe hearing loss are more likely to be employed than those with more severe hearing impairments.
The Gallaudet Research Institute also offers some statistics of its own and other resources, through its demographic fact sheet. Plus, some state governments may maintain their own statistics for the prevalence of hearing loss in the state. For example, the Arizona Commission for the Deaf and Hard of Hearing has estimates on the state's d/hoh population.