The following is a contribution by outside blogger Gregory Sokoloff. Opinions expressed are solely those of Mr. Sokoloff.

It seems to be the most “elusive” statistic American society has to deal with. We know the approximate size of the national bovine herd, we know how many pets live on average in American households. And yet when it comes to illegal immigration, we still cannot produce a credible number.

About 11 million is the statistic juggled most often by Washington politicians and the left-wing media. Others put the number higher. The Pew Hispanic Center has mentioned 12 million while the U.S. Border Patrol union Local 2544 in Tucson, Ariz., issued some time ago a higher estimate: between 12 million and 15 million. The most staggering number so far has come from the financial firm Bear Stearns, which has analyzed the flow of remittances sent abroad and other financial data and reported an estimated 20 million illegal aliens living and working in the United States today.

And there it stands. Interestingly, every year, the U.S. Border Patrol releases its arrest statistics that can shed some light on the matter. According to its reports, nearly 12.3 million people were arrested along the U.S-Mexican border in an attempt to cross it illegally in the 12 years from fiscal 1999 through 2010. Neither the Border Patrol nor the immigration service in Washington would say how many got through. However, many credible experts put the Border Patrol’s success rate at about 20-25 percent, meaning that for every intruder caught three or four are getting through. And if for a moment we accept this formula, it would mean that in the same 12-year period, between 36.9 million and 49.2 million successfully made it through the U.S. Border Patrol dragnet and settled down in the country without any immigration papers. Add this to the 6.7 million illegal aliens, who, according to the Department of Homeland Security, arrived in the country in the 1990s and 1980s, and the number jumps to 43.6 million or 55.9 million – whichever you choose to believe.

Customs and Border Protection spokesman Bill Brooks said the agency “does not subscribe” to this formula. But Sen. John McCain (R.-Ariz.) made a curious admission seven years ago when in a letter to a constituent, he wrote that “according to the U.S. Border Patrol apprehension statistics, it is estimated that almost four million people crossed our borders illegally in 2002.” The esteemed co-sponsor of the now-defunct amnesty proposal would not say how he got this number. But in fiscal 2002, the Border Patrol reported 929,809 arrests, which makes it obvious the senator had either used the x4 formula himself or government officials, who had given him the number in some classified briefing, used it for him.

The Obama administration, while advocating for amnesty, boasts tougher enforcement of immigration laws. Indeed, more that 1.5 million illegals have been removed from the country since fiscal 2008, according to ICE statistics. But the annual deportation numbers are still lower that the generally accepted figure of roughly 500,000 illegals making it into the U.S. every year. Of course, sociologists would argue that any calculations need to factor in people who return to their own countries, multiple entries by the same individuals and so forth. And that is true.

But this does not change the crux of the matter: the only correct and honest answer to the question of how many illegal aliens are currently living in the United States is: We don’t know!

That is why it is imperative for us to empanel — before we start any serious discussion of immigration reform — an independent blue-ribbon commission capable of giving us an honest answer about the number of illegal immigrants we are dealing with. Its conclusions, which may very well surprise many of us, will help us decide what kind of reform, if any, we need.