Citing the ACA's young adult provision, Jonathan Cohn notes that the proportion of uninsured 18-24 year-olds fell by two percentage points last year. Marie Diamond adds that the "Health and Human Services Department had estimated that 1.2 million young adults would sign up for coverage under that provision this year, but early numbers show that the total could be much higher." Cohn points to this bit from Brad Wright:
Historically, economic downturns coincide with increases in the number of uninsured, as people lose their jobs and, thanks to the design of our health care system, their insurance coverage. So, the unchanged number of uninsured masks what actually happened: Roughly 810,000 middle-aged adults, those ages 45 to 64, were likely let go from their jobs, didn't yet qualify for Medicare, and ended up uninsured. Meanwhile, some 494,000 young adults, those ages 18 to 25, gained coverage, which seems to point to the ACA provision allowing children to stay on their parents' plans until age 26 that went into effect in the fall of 2010. Of course, there may be other explanations, but the simplest explanation is likely the right one.