A new study focusing on the chronically ill says the answer is no. Here is Aaron Carroll’s discussion:

The study’s main findings were that patients who were uninsured before reform didn’t have a bigger improvement in total cholesterol, HbA1c level, or systolic blood pressure compared to those who were insured over the entire period. They also looked specifically at patients who had the most potential to see improvement: those who had poorly controlled disease before reform, had no established primary care before reform, and who obtained insurance in the first follow-up year after reform. Even those patients showed no significant improvement over those who were already insured....

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