Homeland Security Secretary Janet Napolitano testified before a Senate committee on Wednesday about issues like border security and the need for improvements to the legal immigration system.
She spoke broadly about the vast strides taken under her watch to both grow and enhance immigration enforcement.
But at the hearing in the Senate Judiciary Committee, some of the most pointed questions came around numbers she couldn't supply.
Here are three metrics that the Department of Homeland Security hasn't yet made available, but would shed a lot of light on the immigration debate:
1. How Many People Overstay Visas Each Year
Border security will likely be a major part of any immigration reform bill. But an estimated 45 percent of undocumented immigrants in the U.S. entered the country legally on a visa, according to the Pew Hispanic Center. Building up the border, therefore, doesn't solve illegal immigration.
During the hearing on Wednesday, Sen. Dianne Feinstein (D-Calif.) asked Napolitano for data on visa overstays, broken down by country. Feinstein said she's been asking for such data "for many years."
"I inquired about this as recently as last week and I was told we should have those in 2013," Napolitano said. "The answer I got was, 'By the end of 2013.'"
Feinstein also asked why a planned system that would use fingerprints to better monitor entries and exits to and from the U.S. hasn't been put into place. Such a system could provide instantaneous data on who is leaving the country.
Napolitano said that a system like that would be "extraordinarily expensive" and would run into "logistical difficulties." Visitors to the U.S. are fingerprinted upon entry, but not upon exit.
DHS does have a system to track immigration exits, but it draws on airplane passenger manifests, not exit fingerprints, to build its database, an official said. The agency also keeps data on the number of visa overstays, but as recently as several years ago, it wasn't very reliable and therefore wasn't released to the public, the official said. The data has improved, however, the official said, and is closer to a potential release.
2. How Much of the Border Is Secure
Sen. Jeff Flake (R-Ariz.) raised questions about the system the Department of Homeland Security (DHS) uses to monitor the state of border security.
"There seems to be confusion within DHS itself or within the Border Patrol as to what constitutes better security or lesser security," Flake said, citing a Rand report. "So you can see as policy makers, we have a difficult time here. It's tough for us to measure."
Until 2010, DHS had been using a system where they looked at the amount of the border that was under "operational control," using factors like intelligence reports and input from senior Border Patrol officials to determine control. Flake called that an "imperfect measure" but "something."
Napolitano said that all parties can agree on the need for a strong and safe border, but didn't get into specifics about how her agency makes those determinations.
DHS was supposed to roll out a new system for measuring border security in 2012, but efforts have been delayed.