From Charles M. Blow's column "Nation of Cowards?" in today's New York Times. I've always believed that a significant element within the dynamic of prejudice against people with disabilities is because many of us are identifiable by sight.
Project Implicit, a virtual laboratory maintained by Harvard, the University of Washington and the University of Virginia, has administered hundreds of thousands of online tests designed to detect hidden racial biases. In tests taken from 2000 to 2006, they found that three-quarters of whites have an implicit pro-white/anti-black bias. (Blacks showed racial biases, too, but unlike whites, they split about evenly between pro-black and pro-white. And, blacks were the most likely of all races to exhibit no bias at all.) In addition, a 2006 study by Harvard researchers published in the journal Psychological Science used these tests to show how this implicit bias is present in white children as young as 6 years old, and how it stays constant into adulthood.