It is hard to say exactly how many people need computer access technology. There are lots of different types of disabilities that can affect one’s ability to use a computer, and obtaining accurate estimates for how many people have disabilities is difficult. Population-wide demographic data are obtained at different times, from different samples of people, using different definitions of disability . Data are usually obtained from surveys and other “self-reporting” mechanisms, which introduces personal and cultural biases into the data. In addition, people can have combinations of disabilities. Finally, it is hard to account for the fact that people with the same diagnosis can have very different abilities.