The foreign-born population share is the most commonly cited statistic in immigration debates. However, immigration policy does not target the foreign-born share. Immigration policy targets flows of migrants. So let’s look at that data.

The most commonly cited data is legal immigration for permanent residence. From 1802 to the 1920s, this essentially meant, “You stepped off the boat in America.” There were some standards of course; criminals, the very poor, the mentally handicapped, those with terminal illnesses, anarchists, and various others were turned away. About 1–5% of arrivals were rejected and deported. Given this, probably people who would have been rejected also were at least partially deterred, but nonetheless, standards for permanent residency were extremely low. Indeed, the reality is that arrivals were treated as if they were entitled to permanent residency, barring certain disqualifying factors. But after restrictive legislation in the 1920s, and especially immigration reforms after WWII and in the 1960s, permanent residency gradually changed from an entitlement with limited conditions, to a special grant that required more extensive application and competition. Here’s permanent residencies granted to new arrivals since 1820:

As you can see, even at their peaks in the 1990s, recent permanent residency grants have been very low as a percentage of U.S. population. I should note here that population percentages are the correct way to represent this data. Sometimes people demand that you tie yourself to a specific number for the appropriate amount of immigration; this is inappropriate for many reasons, but at the most basic level, comparing raw immigration numbers across different years misses the essential fact that the size of the U.S. population changes how many immigrants can be effectively assimilated.

The correct way to describe the 1990s and 2000s is that they saw levels of legal immigration that are, in historic comparison, fairly low, although they are quite high compared to the all-time-lows of the 1930s and 1940s. It should be noted, however, that legal permanent residency grants were rising before the immigration act in the 1960s which eased U.S. immigration policy. Sometimes people act as if one law changing created a wave of U.S. immigration ex nihilo; that’s nonsense. Much of the immigration we’ve observed was a product of modernization and globalization, and recovery from war and depression, not a product of policy changes, although of course policy changes have played a very substantial role.

However, while many people show this data as an indicator of “immigration,” it is incomplete. It turns out that only about half of permanent residencies only go to new arrivals. The other half go to people who already reside in the United States on some other type of visa, and have an “adjustment of status.” Here’s the data from 2013 to 2015 showing new arrivals vs. adjustment of status.

This is important, because it means that “Green Cards” to not mean “Immigration.” A person could have arrived on a student visa and been here 10 years for a full program up to a PhD and then apply for an adjustment of status. That person had been counted in the foreign-born share for a long time and giving them permanent residency or not will not change immigration. Indeed, it could juke the stats in a weird way: if we deny them an adjustment, they leave, and then 10 years later they marry an American, they could show up in inflow data twice.

The point is, adjusting green card policy will not have a huge impact on actual inflows of people. It also may not have a big impact on the foreign-born stock, since the vast majority of people coming to the United States arrive on non-immigrant visas, such as students, H1-B or H2-B workers, diplomats, tourists, and others. Here’s the number of long-term nonimmigrant visas issued each year.

Any of these groups could show up in Census or ACS counts of the foreign-born population. Many could adjust to a green card, some could not. But the point is, student visas have nearly double the impact on regular immigration flows that permanent residencies have, and temporary workers and intercompany transfers are bigger still.

In other words, if you want to know why the foreign-born share is rising, green cards aren’t enough. Indeed, visas aren’t enough, because much immigration is illegal and has no paperwork at all.

Let’s try this another way. Let’s look at not just permanent residency, but total inflows into the United States. We’ll stretch back to 1700. This will include the forced immigration of enslaved people, corrections to the pre-1906 immigration figures to account for known omissions of certain passenger classes and origin points, and inclusion of illegal immigration in the 20th and 21st centuries. Undoubtedly the data below will have errors, but it should give us a much clearer idea of what’s happening with immigration.

Based on this data, we have seen major immigration waves in the pre-revolutionary period, the 1830–1920 period, and the 1960-present period. Immigration has fallen by about 50% since its peak around 1990–2006, entirely due to lower illegal immigration. Let me reiterate this point: illegal immigration has fallen by a very large amount.

However, this data may still be incorrect, as it uses permanent residency as its base for legal inflows. An alternative method would be to use inflows as reported in major surveys like Census, ACS, or CPS. Here’s data using that method. We can get various migration estimates back to 1940 for some years, and can ruthlessly extrapolate between missing years to get a very broad estimate of immigration. This reflects both legal and illegal immigration, for permanent residence or otherwise. I have created a harmonized estimate from various surveys; as above, any curious experts reading are welcome to ask and I’ll provide underlying data.

And here, since 1940, is the survey-based estimate vs. the category-based estimate:

They are both quite different. What I find notable is that 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.

For current debates, however, the relevant conclusion is identical in both.

Current immigration rates are between 28% and 65% below their post-WWII peak annual levels, or between 25% and 45% below their post-WWII peak decadal levels.

Any serious analyst of immigration committed to an honest presentation of the facts must grant that immigration right now is not particularly high compared to recent, living memory.