WHICH MOSTLY DEMONSTRATES THE NARROW BAND WITHIN WHICH OUR TAXES FLUCTUATE:

The Revenue Limits of Tax and Spend: Whether rates are high or low, evidence shows our tax system won't collect more than 20% of GDP. (DAVID RANSON, 5/17/10, WSJ)

"Hauser's Law," as I call this formula, reveals a kind of capacity ceiling for federal tax receipts at about 19% of GDP.

What's the origin of this limit beyond which it is impossible to extract any more revenue from tax payers? The tax base is not something that the government can kick around at will. It represents a living economic system that makes its own collective choices. In a tax code of 70,000 pages there are innumerable ways for high-income earners to seek out and use ambiguities and loopholes. The more they are incentivized to make an effort to game the system, the less the federal government will get to collect. That would explain why, as Mr. Hauser has shown, conventional methods of forecasting tax receipts from increases in future tax rates are prone to over-predict revenue.

For budget planning it's wiser and safer to assume that tax receipts will remain at a historically realistic ratio to GDP no matter how tax rates are manipulated. That leads me to conclude that current projections of federal revenue are, once again, unrealistically high.

Like other empirical "laws," Hauser's Law predicts within a range of approximation. Changes in marginal tax rates do not make a perceptible difference to the ratio of revenue to GDP, but recessions do. When GDP falls relative to its potential, tax revenue falls even more. History shows that, in an economy with no "output gap" between GDP and potential GDP, a ratio of federal revenue to GDP of no more than 18.3% would be realistic.

In this form, Hauser's Law provides a simple basis for testing the validity of any government's revenue projections. Today, since the economy already suffers from a large output gap that is expected to take many years to close, 18.3% must be a realistic upper limit on the ratio of budget revenues to GDP for years to come. Any major tax increase will reduce GDP and therefore revenues too.

But CBO projections based on the current budget show this ratio reaching 18.3% as early as 2013 and rising to 19.6% in 2020.