"No matter what the tax rates have been, in postwar America tax revenues have remained at about 19.5% of GDP." What a pity that his discovery has not been more widely disseminated.
The chart nearby, updating the evidence to 2007, confirms Hauser's Law. The federal tax "yield" (revenues divided by GDP) has remained close to 19.5%, even as the top tax bracket was brought down from 91% to the present 35%. This is what scientists call an "independence theorem," and it cuts the Gordian Knot of tax policy debate.
What happens if we instead raise tax rates? Economists of all persuasions accept that a tax rate hike will reduce GDP, in which case Hauser's Law says it will also lower tax revenue. That's a highly inconvenient truth for redistributive tax policy, and it flies in the face of deeply felt beliefs about social justice. It would surely be unpopular today with those presidential candidates who plan to raise tax rates on the rich – if they knew about it.
Although Hauser's Law sounds like a restatement of the Laffer Curve (and Mr. Hauser did cite Arthur Laffer in his original article), it has independent validity. Because Mr. Laffer's curve is a theoretical insight, theoreticians find it easy to quibble with. Test cases, where the economy responds to a tax change, always lend themselves to many alternative explanations. Conventional economists, despite immense publicity, have yet to swallow the Laffer Curve. When it is mentioned at all by critics, it is often as an object of scorn.
Because Mr. Hauser's horizontal straight line is a simple fact, it is ultimately far more compelling. It also presents a major opportunity. It seems likely that the tax system could maintain a 19.5% yield with a top bracket even lower than 35%.
What makes Hauser's Law work? For supply-siders there is no mystery. As Mr. Hauser said: "Raising taxes encourages taxpayers to shift, hide and underreport income. . . . Higher taxes reduce the incentives to work, produce, invest and save, thereby dampening overall economic activity and job creation."