It turns out that someone ran the numbers. Measuring the Sacrifice of Open Borders This experiment presumes that the only two drivers of national income per capita are national average IQ and an unexplained productivity residual.The unexplained productivity residual plays a key role in the case for Open Borders, and I critique that residual. I use the same constant returns to scale framework as Caplan, in which the migration of every human being to the United States would increase global output per capita by about 80%. I then estimate that in the benchmark model, where IQ's social return is much larger than its private return,the per-capita income of current U.S. residents would permanently fall by about 40%. This is not an arithmetic fallacy: this is the average causal effect of Open Borders on the incomes of ex-ante Americans. A 40% drop in income. Not bad, I thought it would be much worse considering that would drive down wage rates to the bottom.