In his State of the Union address, President Bush proposed tax cuts to make health insurance more affordable for the uninsured. The next day, Stephen Colbert had this to say on his show on Comedy Central: “It’s so simple. Most people who can’t afford health insurance also are too poor to owe taxes. But if you give them a deduction from the taxes they don’t owe, they can use the money they’re not getting back from what they haven’t given to buy the health care they can’t afford.”

Just so. As health economists have long known, market incentives induce private insurers to spend vast sums to avoid people who may actually require health care. This problem is mitigated (though not eliminated) by employer-provided group policies. Because Mr. Bush’s proposal would steer people toward individual policies, it would actually strengthen the incentive to shun unhealthy people. Such people can now keep their insurance by not changing jobs. But no private company would want them as individual policyholders at a price anyone could afford.

That Mr. Bush’s proposal will not shrink the ranks of the uninsured is not its most serious problem. Far more troubling is its embrace of a system under which we spend more than twice as much on health care, on average, as the 21 countries in which life expectancy exceeds ours. American costs are so high in part because the reliance on private insurance multiplies administrative expenses, currently about 31 percent of total outlays.

Most health economists agree that government-financed reimbursement is the only practical way to control these expenses, many of them stemming from insurers’ efforts to identify and avoid unhealthy people. Canada’s single-payer health system, which covers everyone, spends less than 17 percent on administrative expenses.