 Well, they're limited. We have the census data, of course, and in Mexico they ask Mexican citizens in their census if they've been to the United States in the last five years, and so we know about return migrants who've been to the United States, who are in Mexico, and then US Census asks where you were born, and so we know the number of you were born in Mexico. We also know the number of people who entered in the past five years, and that gives you some data on who are coming and going. And then on the US side, there's immigration statistics system, which is basically entries. So we know how many people enter with permanent resident visas, temporary work visas, business visas, exchange visas, and so on. And so that's about the extent of the official statistics system. Then there are a lot of private efforts, like I run the Mexican Migration Project, and we've been collecting data on documented and undocumented migration from Mexico to the US for about 30 years, and every year we do a new round of surveys. And with this data set, we can really characterize and follow the trajectory of both documented and undocumented migration over time and let them see the dynamics underneath the flows that we observe in the official statistics. But that's a project that I've been running with my colleague in Mexico, Jorge Durand, and so it's not part of the government statistics system. I think if we had a migration module on the American surveys, like the current population survey, which is done every month, if they had more questions on migration, and particularly in the census, we need to ask a question on place of birth of parents, which was eliminated from the US census in 1970. And so now we have about a quarter of the population in first or second generation of immigrant status, and the second generation is crucial to see how immigrants are adapting and integrating, and there's no data on a nationwide source of large sample of Americans on the second generation. It's a big defect in our statistical system. So simply adding a question to the census or the American community survey on parental birthplace would help us quite a bit. One of the lessons that come out of my work is that statistical systems and official data can't do it all, and so there's always a place for researchers launching their own research projects to gather data that explain the trends, that go behind the trends to look at the dynamics underlying what you observe from national level statistics, and that's what I've tried to do over the course of my career with the Mexican migration project.