From What Explains Variation In Disability Application Rates Across States, a report by the Center for Retirement Research at Boston College (see below for an illustration from the report):
This brief has examined why SSDI [Social Security Disability Insurance] application rates vary so much between states. Not surprisingly, health, demographic, and employment characteristics are the major determinants of this state variation, explaining over 70 percent of the variation in total SSDI application rates. In addition, having state-mandated private TDI [Temporary Disability Insurance] is associated with lower application rates, and the governor’s political party [slightly fewer claims in states with Republican governors] is also correlated with the application rate. In short, the health, demographic, and employment characteristics of a state – not state policies or politics – explain most of the variation across states.