In the midst of the Senate debate on an immigration bill this month, the Heritage Foundation published a report claiming that legalization of undocumented workers already here and creation of a temporary-worker program would unleash a flood of more than 100 million new immigrants in the next 20 years. The headline-catching number turned heads on Capitol Hill, provided grist for talk radio, and hardened the opposition to immigration reform.

In hindsight, however, the number looks less and less plausible. Consider: If immigrants did come in such numbers, the average would be 5 million a year. That compares to an average immigration inflow, legal and illegal, of about 1.5 million during the past decade. The U.S. economy simply could not produce enough jobs each year during the next two decades to attract and employ that many immigrants. We also know from experience that previous attempts at legalization did not unleash a flood of so-called chain migration, in which newly legalized and naturalized workers sponsor spouses, children, parents and siblings. Check out an op-ed article posted today on the Cato web site that spells out in detail why the 103 million figure is a gross exaggeration.

The Congressional Budget Office, in its own study [.pdf] released May 16, calculates that immigration reform along the lines of what the Senate passed last week would increase immigration over the next decade by less than 8 million. And an analysis by the President’s Council of Economic Advisers found numerous methodological faults with the Heritage study, including double counting and failure to account for emigration.

The Heritage study generated a lot of heat in an already over-heated immigration debate. Unfortunately, it failed to provide any real light.