AS THEY TACK left and right state by state, the Democratic presidential contenders can't agree on much. But one cause they all support — along with Republicans such as former Massachusetts Gov. Mitt Romney and California's own Gov. Arnold Schwarzenegger — is universal health coverage. And all of them are wrong.

What these politicians and many other Americans fail to understand is that there's a big difference between universal coverage and actual access to medical care.

Simply saying that people have health insurance is meaningless. Many countries provide universal insurance but deny critical procedures to patients who need them. Britain's Department of Health reported in 2006 that at any given time, nearly 900,000 Britons are waiting for admission to National Health Service hospitals, and shortages force the cancellation of more than 50,000 operations each year. In Sweden, the wait for heart surgery can be as long as 25 weeks, and the average wait for hip replacement surgery is more than a year. Many of these individuals suffer chronic pain, and judging by the numbers, some will probably die awaiting treatment. In a 2005 ruling of the Canadian Supreme Court, Chief Justice Beverly McLachlin wrote that "access to a waiting list is not access to healthcare."

Supporters of universal coverage fear that people without health insurance will be denied the healthcare they need. Of course, all Americans already have access to at least emergency care. Hospitals are legally obligated to provide care regardless of ability to pay, and although physicians do not face the same legal requirements, we do not hear of many who are willing to deny treatment because a patient lacks insurance.

You may think it is self-evident that the uninsured may forgo preventive care or receive a lower quality of care. And yet, in reviewing all the academic literature on the subject, Helen Levy of the University of Michigan's Economic Research Initiative on the Uninsured, and David Meltzer of the University of Chicago, were unable to establish a "causal relationship" between health insurance and better health. Believe it or not, there is "no evidence," Levy and Meltzer wrote, that expanding insurance coverage is a cost-effective way to promote health. Similarly, a study published in the New England Journal of Medicine last year found that, although far too many Americans were not receiving the appropriate standard of care, "health insurance status was largely unrelated to the quality of care."

Another common concern is that the young and healthy will go without insurance, leaving a risk pool of older and sicker people. This results in higher insurance premiums for those who are insured. But that's only true if the law forbids insurers from charging their customers according to the cost of covering them. If companies can charge more to cover people who are likely to need more care — smokers, the elderly, etc. — then it won't make any difference who does or doesn't buy insurance.

Finally, some suggest that when people without health insurance receive treatment, the cost of their care is passed along to the rest of us. This is undeniably true. Yet, it is a manageable problem. According to Jack Hadley and John Holahan of the left-leaning Urban Institute, uncompensated care for the uninsured amounts to less than 3% of total healthcare spending — a real cost, no doubt, but hardly a crisis.

Everyone agrees that far too many Americans lack health insurance. But covering the uninsured comes about as a byproduct of getting other things right. The real danger is that our national obsession with universal coverage will lead us to neglect reforms — such as enacting a standard health insurance deduction, expanding health savings accounts and deregulating insurance markets — that could truly expand coverage, improve quality and make care more affordable

As H. L. Mencken said: "For every problem, there is a solution that is simple, elegant, and wrong." Universal healthcare is a textbook case.

MICHAEL TANNER is director of health and welfare studies and MICHAEL CANNON is director of health policy studies at the Cato Institute.