As we recently wrote, it’s better for patients to have Medicaid than to be uninsured, contrary to critics of the program. But is having Medicaid, as those critics also say, much worse than having private insurance?

This idea has become a talking point for conservatives who back big changes to Medicaid, as the Senate health bill proposes. The poor would benefit simply by being ushered off Medicaid and onto private insurance, they write.

But it’s far from proven that Medicaid is worse than private insurance. A lot depends on what kind of insurance is compared with Medicaid, and how they are compared.

Many studies that measure Medicaid against private insurance suffer from the same flaws that compare Medicaid with being uninsured. They’re terribly confounded, and can show only associations, not causation. People with private insurance are healthier and wealthier than those on Medicaid, and in ways not fully controlled for in statistical analyses. These factors almost certainly predispose someone on Medicaid to have worse outcomes than someone with private insurance.