We've written a fair bit about the economic aspects of immigration over the past few months. But what do members of Congress think about the subject? And what sorts of experts are they listening to?

There will be hearings. (Photo by John Moore/Getty Images)

Here's some insight: On Wednesday and Thursday this week, the U.S. Congress Joint Economic Committee held a two-day hearing on the economics of immigration — and on the potential impact of the Senate immigration bill now on the table. The hearing was well attended and co-chaired by  Sen. Amy Klobuchar (D-Minn.) and Rep. Kevin Brady (R-Tex.)

Two of the witnesses clearly favored expanding immigration, including tax reformist Grover Norquist and Georgetown economist Adriana Kugler. Another was supportive but skeptical — Madeline Zavodny, an economist at Agnes Scott College. The last, Steven Camarota of the Center for Immigration Studies, was strictly opposed. Here are some highlights:

1) Grover Norquist is not a fan of that Heritage study.

Like many pro-immigration conservatives, Norquist sharply criticized a recent Heritage study suggesting that immigration reform would cost the government $5.3 trillion. Among other objections, Norquist noted that 40 percent of this price tag included the costs of educating immigrants, the vast majority of whom are already here, albeit illegally. "Much of the costs which they attribute are there, anyway," he said.

Norquist also went into a mini-digression on the history of the Heritage Foundation, which, he noted, had long been in favor of immigration reform — dating back to this 1984 brief by economist Julian Simon.  "It's only since 2007 that one guy over at Heritage had a different opinion," Norquist said, referring to welfare policy expert Robert Rector.

2) There was widespread agreement that a path to citizenship would be a huge economic boon for the 11 million undocumented immigrants who are already here. 

(Sarah L. Voisin / The Washington Post)

"There are small income gains — I would say 6 to 13 percent — when people are able to legalize their status, as happened after [the 1986 immigration reform]," said Madeleine Zavodny, who chairs the economics department at Agnes Scott College.

Georgetown's Adriana Kugler went further. "We know that as a result of the legalization and eventual citizenship after 13 years, there would be a 25 percent gain in earnings and in income that would increase, of course, the tax revenues that we would be obtaining from this population. So, legalization in itself is something that we would contribute to solve some of our fiscal issues."

3) Participants also agreed on the value of bringing more highly educated immigrants into the United States.

Russian-born Google co-founder Sergey Brin (David Paul Morris / Bloomberg)

"For example, research by Jennifer Hunt shows that highly educated immigrants earn patents at more than twice the rate of highly educated natives," said Zavodny. "This contribution is most notable in the high-tech sector, where immigrants were key founders in a quarter of U.S. hightech startups in recent years, and half of high-tech start-ups in Silicon Valley."

In her view, there was no question that we should be prioritizing these immigrants. "I think there are some groups to whom you would want to give permanent residency right away, and that would be those with extraordinary ability. Say, PhD holders, STEM graduates of U.S. colleges and universities, workers like that."

4) But there was more debate over the value of low-skilled immigrants.

We'll probably need some immigrants here, too. (ISTOCKPHOTO)

Granted, there's more to the economy than Silicon Valley. Georgetown's Kugler argued that the United States will have plenty of jobs in the years ahead that don't require advanced degrees — and those are places where immigrants could be valuable.

"Some of those jobs in health, the ones that are growing the fastest and that are expected to grow the fastest in the next ten years, do not necessarily even require a college education," Kugler said. "There are some important skilled jobs in information, for computer science. Again, those, some of those jobs are not requiring necessarily very high levels of education."

But Zavodny was more skeptical — particularly of the idea that Congress should offer more visas based on family ties, which tends to favor low-skilled workers. "If the priority is economic growth," she said, "and these days it really does need to be, then there needs to be greater emphasis on the employment side at least for now, instead of on the family ties." She suggested it might be better to restrict visas only to those who had job offers.

(Elsewhere in the hearing, Zavodny approved of the fact that the Senate bill would reduce the number of family-based visas, by eliminating visas for siblings and adult married children of citizens and permanent residents after 18 months.)

5) Several members of Congress were skeptical of the notion that immigrants don't take American jobs.

Rep. Richard Hanna (R-N.Y.) asked about the widespread belief among economists that immigrants don't really take jobs from Americans. "Much immigrant labor is highly skilled and thus presumably not differentiated," he said. "Why would wage competition not incur in the labor market?"

Norquist argued that many high-tech workers in the United States are already in competition with high-tech workers from around the world. The only question is whether we bring those workers here. "Microsoft has people they hire and they put in Canada because they can't get them across the border here," he said. "So they pay taxes in Canada and make the Canadian economy stronger."

Kugler tackled the question as it pertained to workers in other parts of the economy. "We actually find very little evidence of displacement," she said." "If anything, there are positive impacts on the earnings of the native-born, not only in other sectors, but also because, as I said before, [immigrants] are also consumers. So, for example, in retail, there are huge increases in employment once the immigrants come into local communities."

Indeed, Kugler added, the studies — like those from George Borjas — that argue that increased immigration has a negative impact on native-born wages tend to assume that these workers are perfect substitutes."Once you’re making that assumption," she said, "you know the results are going to give what they give."

6) There was also some debate over how well the children of immigrants fare in this country.

Also discussed at the hearing. (The Washington Post)

The Center for Immigration Studies tends to take a negative view of immigration. As such, Camarota predicted that plenty of bad things would happen if the United States legalized the 11 million or so illegal immigrants currently in the country.

"About 31 percent of all children born to immigrants today are born to a mother who has not graduated high school," he said. "Those kids, as far as we can tell, are really going to struggle. And that does describe a large fraction of the illegal population."

At that point, Zavodny cut in. "I would disagree," she said. "I think the evidence shows quite clearly that the second generation of the children of immigrants tend to do not only better than their parents, but better than the children of similarly poorly off natives."

7) There was also a running argument about whether the United States needed more immigration to avoid turning into Japan.

Japanese Prime Minister Shinzo Abe. (ISSEI KATO/REUTERS)

Japan is aging fast — leaving fewer workers to support a greater number of retirees. Norquist argued that the country is hurt by restrictive immigration laws: "I went to business school in the 1980s, and all I heard from everybody was that Japan is number one, they're going to leave us in the dust," he said. "And all of a sudden they left the playing field, because one, they forgot to have kids, and two, they're not capable of doing immigration."

Still, Steven Camarota of the Center for Immigration Studies was skeptical that the immigration bill being considered in the Senate would have a massive effect on America's age structure: "The immigrants have more children, somewhat, and they do pull it up, but not much. Over the next 40 years, a million or a million-and-a-half immigrants a year might offset the aging of the U.S. population by 10 or 15 percent."

Further reading:

--Five things economists know about immigration.

--Here's our rundown of the initial draft of the Senate immigration bill. And here's a report on some of the amendments now being added to the bill.