When asked why he robbed banks, Willie Sutton famously replied, “Because that’s where the money is.” The same logic explains the call by John Edwards, the Democratic presidential candidate, for higher taxes on top earners to underwrite his proposal for universal health coverage.

Providing universal coverage will be expensive. With the median wage, adjusted for inflation, lower now than in 1980, most middle-class families cannot afford additional taxes. In contrast, the top tenth of 1 percent of earners today make about four times as much as in 1980, while those higher up have enjoyed even larger gains. Chief executives of large American companies, for example, earn more than 10 times what they did in 1980. In short, top earners are where the money is. Universal health coverage cannot happen unless they pay higher taxes.

Trickle-down theorists are quick to object that higher taxes would cause top earners to work less and take fewer risks, thereby stifling economic growth. In their familiar rhetorical flourish, they insist that a more progressive tax system would kill the geese that lay the golden eggs. On close examination, however, this claim is supported neither by economic theory nor by empirical evidence.

The surface plausibility of trickle-down theory owes much to the fact that it appears to follow from the time-honored belief that people respond to incentives. Because higher taxes on top earners reduce the reward for effort, it seems reasonable that they would induce people to work less, as trickle-down theorists claim. As every economics textbook makes clear, however, a decline in after-tax wages also exerts a second, opposing effect. By making people feel poorer, it provides them with an incentive to recoup their income loss by working harder than before. Economic theory says nothing about which of these offsetting effects may dominate.