From Lyman Stone:
…the survey-based immigration method finds essentially no increase in immigration after the immigration reforms of the 1960s: indeed inflow rates may have declined. The implication here is that rising foreign-born population has its roots well before any changes to immigration law, and may be as much about declining outflows as it is about rising inflows.
Notably, both estimates give a similar 1940-Present estimate of average annual migration: 0.51% for the survey method, 0.57% for the category method. The category method is inflated by that bump around the 1950s, which was largely temporary, seasonal illegal immigration. Adjusted for that, it’s about 0.52%. In other words, both methods give similar long-run migration rates, at a long-run average level somewhat lower to the long-run average level in the previous migration period.
But the trend is different. The survey-based method suggests immigration rates peaked around 1970 and have fallen since. The category-based method suggests that immigration rates peaked in the 1990s, and have fallen since.
The longer piece covers a variety of other related topics, including stocks in addition to flows (longer lives and lower native fertility skew the stock), and the connection between immigration and pro-natalist policies. Via Ross Douthat.