How Health care works now.

Private markets for health insurance, left to their own devices, work very badly: insurers deny as many claims as possible, and they also try to avoid covering people who are likely to need care. Horror stories are legion: the insurance company that refused to pay for urgently needed cancer surgery because of questions about the patient’s acne treatment; the healthy young woman denied coverage because she briefly saw a psychologist after breaking up with her boyfriend.

And in their efforts to avoid “medical losses,” the industry term for paying medical bills, insurers spend much of the money taken in through premiums not on medical treatment, but on “underwriting” — screening out people likely to make insurance claims. In the individual insurance market, where people buy insurance directly rather than getting it through their employers, so much money goes into underwriting and other expenses that only around 70 cents of each premium dollar actually goes to care.

Still, most Americans do have health insurance, and are reasonably satisfied with it. How is that possible, when insurance markets work so badly? The answer is government intervention.

Most obviously, the government directly provides insurance via Medicare and other programs. Before Medicare was established, more than 40 percent of elderly Americans lacked any kind of health insurance.

Today, Medicare — which is, by the way, one of those “single payer” systems conservatives love to demonize — covers everyone 65 and older. And surveys show that Medicare recipients, a government plan, are much more satisfied with their coverage than Americans with private insurance.