A study on employment and adults with autism just came out in May. This is specifically about young adults, though I have some thoughts on the subject more broadly.
What I found especially interesting was that adults with other developmental disabilities (e.g. some degree of mental retardation) have a higher rate of employment. That made some sense to me, as there does seem to be more services set up for people with Down's Syndrome and other such conditions. Also society as a whole may better understand these disabilities. Autism is more difficult to wrap one's head around.
Since I have a degree in political science, I've been trained to be skeptical of statistics. How did they get these numbers? What methods did they use?
First off, the unemployment rate in general only includes people applying for unemployment benefits or report looking for work. People who have given up or taken a major break in job searching aren't included- that would describe many people with disabilities.
Other factors: many adults on the spectrum especially past 35 or so, are unlabeled. In fact, probably most of them. Some of them fall under the radar, as they may have better adjusted to mainstream society, or maybe dropped out of high school, or are homeless or move frequently due to poverty.