Innumeracy and immigration

How many illegal immigrants are there in this country? This question has relevance not only for those of us who use population data but it is also a warning against uncritically accepting numbers just because they are frequently repeated.

During the immigration debate over the summer leading to the mass protests on May 1, the number "3 million" was constantly repeated: there are 3 million illegal immigrants coming into this country every year. A moment's thought should reveal why this number is problematic.

First, the total number of illegal immigrants is also often cited as being around 11 million. Both numbers can't be right.

Second, the figure has its origins with the border agents who say they apprehend about 1 million people annually, and estimate that three times as many actually make it across. As the mathematician John Allen Paulos (author of Innumeracy) this number is based on the number of apprehensions they make, and this includes many people who try repeatedly to cross the border. Additionally, their estimate that 3 times as many go unapprehended is of course just that--an estimate.

Numeracy in GIS is as important as graphicacy, and like maps numbers are political. It's advisable to always ask "in whose interest is this number produced? Under what circumstances was the number produced?"