March 25 (Bloomberg) -- At a hearing last week in the U.S. House of Representatives, lawmakers expressed dismay that Homeland Security officials had yet to devise a simple metric to measure border security. Indeed, the officials did their best to avoid being pinned down by a Homeland Security subcommittee, which met more than two years after their department promised to produce a metric.

“While enforcement statistics and economic indicators point to increased security and improved quality of life,” their joint testimony states, “no single metric can conclusively define the state of border security.”

It’s not clear what exactly Border and Maritime Subcommittee chairwoman Candice Miller of Michigan and ranking member Sheila Jackson Lee of Texas were expecting. Maybe the crime rate in San Diego multiplied by the gross domestic product in El Paso, divided by the number of apprehensions in Nogales, Arizona? Good luck. Any “measurement” of border security would be a bogus trick.

The danger is that a metric might have to be conjured to win passage of comprehensive immigration reform. Many members of Congress insist that any path to citizenship for the estimated 11 million undocumented people in the U.S. be predicated on quantifying the security of the nation’s 7,000 miles of land borders and 95,000 miles of coastline.

“We need to have a measurement,” Senator John McCain said in a hearing this month. Well, here are some numbers: The Border Patrol has more than doubled in size since 2004, to more than 21,000 agents. Electronic surveillance has expanded exponentially. In 2012, the Border Patrol recorded 364,768 apprehensions, down 50 percent from four years earlier -- a sign of success because fewer apprehensions with beefed up security are a result of fewer attempts. All signs point to a significantly more secure border than the U.S. has ever had.

But the nature of covert activity, including human beings darting through the night, is that it’s hard to read exactly what’s going on. Because the goal itself is impossible, the means of measuring its achievement will have to be very flexible indeed. The question then, is whether immigration hardliners will be willing to accept a series of facts -- apprehensions, border control staffing and the like -- that paint an impressionistic picture of border security. Or whether they will insist on a form of metric flimflam that promises a degree of specificity about illegal border crossings that no data can accurately deliver.

It’s no surprise that the Department of Homeland Security isn’t eager to lend its databases and analytics to a border security charade. Pity then, that for the nation to get a sensible immigration reform, it just might have to.

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