(Jacquelyn Martin/AP)

But Medicaid does, sometimes, allow for natural experiments. And a team of researchers in Ohio have found an interesting way to explore how Medicaid coverage impacts on the prognosis of a patient diagnosed with cancer. Their study, to be published next month in the journal Cancer, finds that while Medicaid coverage prior to a cancer diagnosis does correlate with a better outcome than no coverage at all, patients in the entitlement program have worse survival rates than Americans with private insurance, or no insurance at all.

Researchers Siran Koroukian, Paul Bakaki and Derek Raghavan linked records from the Ohio Cancer Incidence Surveillance System with Ohio Medicaid enrollment data, to get a unique look at Medicaid and non-Medicaid patients’ survival rates in the face of a cancer diagnosis. The study focused on eight potentially curable cancers, such as lung cancer and melanoma. It also segregated Medicaid enrollees into two categories, those who were enrolled at the time of their diagnosis, vs. those who enrolled afterwards, to get a more detailed sense of how coverage impacts outcomes.

The bad news first: Medicaid patients had worse survival rates than the rest of the study sample, which included both those with private insurance and with no coverage at all. The disparities persisted even after the researchers controlled for where patients live, how much education they had received and the income level of their neighborhoods.

But the good news is that patients who were enrolled in the program prior to their cancer diagnosis tended to do better than those who sign up after learning of their disease. This suggests to the authors that longer enrollment in the entitlement program “may be associated with a greater ability on the part of the beneficiary to develop a network of providers and an ability to navigate the system.” Previous studies have found longer enrollment in Medicaid to also correlate with increased access to some cancer screenings, such as mammograms.

What this study doesn’t delve into is why Medicaid enrollees have worse outcomes than the general population, whether it has to do with access to certain physicians, with wait times to see a specialist, or some issue completely removed from the doctor’s office.

The disparities in outcomes could also have a lot to do with some factors that the researchers couldn’t control for: Whether Medicaid patients are more likely to have other health-care issues, or if they have less of a supportive social network in seeking treatment. “I don’t think we were able to capture the greater level of vulnerability that Medicaid patients face,” says Koroukian, the study’s lead author. And that could also play a role in why Medicaid patients face worse outcomes in cancer treatments than their non-Medicaid counterparts.