Immigration Policy and the Two Types of Errors

When screening applicants, there are two ways to make a mistake. A Type I error occurs when someone who should be rejected is admitted. A Type II error occurs when someone who should be admitted is rejected. Immigration policy faces this tradeoff. Tightening screening and admission requirements may reduce the first type of error, but it can also increase the second. The challenge is to balance the costs of admitting someone who should not enter against the costs of excluding someone who could benefit the country.

The stated Trump administration immigration policy has been to reduce Type I errors, reduce illegal immigration. Collateral damage is an increase in Type II errors, fewer legal immigrants. The Cato Institute reports that legal immigration fell substantially more than illegal immigration. Comparing monthly entry figures through February 2026 with those before Trump took office, Cato estimates that legal entries fell by approximately 145,000, while illegal entries fell by about 53,000. The restrictions affect people seeking admission through established legal channels, including employment, family reunification, and education. A full error cost analysis would require an estimate of the cost to society of typical illegal entrants and the lost benefit of typical legal entrants. It is open to debate, but evidence suggests that immigration is a net positive and that illegal immigrants to the US are not a cost.

One frequently hears that potential immigrants should simply follow the legal process. This offers little guidance if that too is unavailable.