In recent years, a growing number of patients who are on Medicaid or Medicare cannot find physicians willing to treat them. In a pilot study, researchers found 95% of the surveyed primary care physicians are willing to accept new patients with private insurance (e.g., Aetna, United, etc.), 78% accept new Medicare patients, and only 13% accept new Medicaid patients.

What causes this inequality in health care access?

(Note: you don't have to draw a graph, but drawing a graph is fine.)