This is a very good data insight.
… The Obama administration for years has been pleading with states to expand their Medicaid programs and offer health coverage to low-income people. Now it has a further argument in its favor: Expansion of Medicaid could lower insurance prices for everyone else.
… By comparing counties across state borders, and adjusting for several differences between them, the researchers calculated that expanding Medicaid meant marketplace premiums that were 7 percent lower.
Reference: Expanding Medicaid may lower all premiums