Paying for Disability

I loved Alex Tabarrok's intro to Paying for Disability:

The number of disabled people in the United States is increasing at a shocking rate — from 1984 to 2000 the number of disabled people more than doubled from 3.8 to 7.7 million. Today, over 5% of adults aged 25 to 64 are disabled. Even more worrying is that disability is increasing especially rapidly among the young. What is responsible for this awful increase? Workplace accidents? Chemicals in the environment? Gun violence? Naahh, it's incentives of course.

By disabled I mean receiving Social Security Disability Insurance or Social Security Income.