As we debate immigration policy, it’s useful to get an idea of how many people from which countries would like to immigrate to the United States. Gallup has conducted a worldwide survey (covering countries with 98% of the world’s population) with 501,000 (!) respondents. It finds that 630 million people would like to immigrate and 138 million would like to come to the United States. That’s 44% of the Census Bureau’s July 2012 estimate of the nation’s current population.

Where do these potential immigrants live now? Gallup lists the 12 countries with 3 million or more. Most are from Asia (China 19m, India 10m, Bangladesh 6m, Philippines 4m, Japan 4m) and Africa (Nigeria 13m, Kenya 3m, Ghana 3m). These figures are far, far higher than the number of immigrants we get from these countries; my understanding is that we get almost no immigrants from Japan, for example.

The most eyecatching numbers here are those from Latin America (Brazil 6m, Mexico 5m, Colombia 3m). Of course the Latin American and Caribbean total is obviously much higher because there are many smaller countries there. As Gallup notes, between 11% of 28% of adults in seven countries—the Dominican Republic, Haiti, Honduras, El Salvador, Jamaica, Guatemala, Nicaragua—say they’d like to immigrate to the United States. But the most important country here is Mexico, which over the 1982-2007 quarter century accounted for 60% of Western Hemisphere immigrants to the United States and 60% of total illegal immigrants to the United States. Immigrants from Mexico are significantly more downscale, in education, skill levels and law-abidingness, than immigrants from any other country—a fact easily explained by their easier access to the United States across our 2,000-mile land-and-shallow-river border.

As blogger Steve Sailer notes, a Pew Hispanic Center survey in 2005, near the peak of the housing bubble, reported that 22 million Mexicans would immigrate to the United States as legal guest workers if that was possible. The Pew and Gallup numbers are not commensurate, since Pew asked a hypothetical question and Gallup asked about general desire to immigrate, but there’s a huge difference between 22 million and 5 million. In the debate on immigration policy Sailer and Mickey Kaus have argued that large-scale illegal immigration from Mexico will likely resume when the U.S. economy revives and if a comprehensive immigration law provides legal status for many or most current illegal immigrants. I have predicted that we will never see the kind of large-scale Mexican immigration to the United States that we saw in 1982-2007. I think the Gallup numbers tend to support my prediction. Desire to immigrate does not usually yield a decision to immigrate. People take the plunge of immigration not just to make money but to pursue dreams or escape nightmares. For Mexicans these days the United States is less of a dream and Mexico is less of a nightmare than in the years from 1982 to 2007.

Test case: Puerto Rico. The huge influx of Puerto Ricans to New York City that started in the late 1940s abruptly ended in 1961, when incomes in Puerto Rico reached one-third the U.S. mainland income level. There were and are no legal barriers for Puerto Ricans, who are U.S. citizens under an act of Congress passed in 1917. They just stopped coming. Recent years have seen some movement of Puerto Ricans to the Mainland (probably more to metro Orlando than metro New York), but it’s nothing like the magnitude of the 1949-61 migration. The data suggested that Mexicans just stopped coming to the United States in 2007, when the housing bubble burst and the recession began. I’m betting—aware of the nontrivial possibility that I could be wrong—that we won’t see another massive wave of immigration from Mexico.