This is according to a Urban Institute study by Karpman, Long and Zuckerman (2016). They look at changes in the uninsurance rate and in the rate of full-year insurance coverage for nonelderly adults (ages 18 to 64) overall and by state Medicaid expansion status. They found that:
The uninsurance rate for nonelderly adults fell from 17.6 percent in September 2013 to 9.9 percent in March 2016, a 43.8 percent decline representing 15.5 million fewer uninsured adults.
Additionally, we see the largest drop among the lowest income individuals in Medicaid expansion states.
Was there any question about this?
The question is, will outcomes be improved? Rates of insurance isn’t what’s important; access (in terms of price) and outcomes (in terms of health) are what matters.