# Airline Screening List Mathematics

What do Santa Claus and DHS have in common? They both keep a list of who’s naughty or nice. DHS’s list isn’t quite as large as Santa’s, but it’s getting quite big. From the AFP:

A watchlist of possible terror suspects distributed by the US government to airlines for pre-flight checks is now 80,000 names long, a Swedish newspaper reported, citing European air industry sources.

The classified list, which carried just 16 names before the September 11, 2001 attacks in New York and Washington had grown to 1,000 by the end of 2001, to 40,000 a year later and now stands at 80,000, Svenska Dagbladet reported.

Airlines must check each passenger flying to a US destination against the list, and contact the US Department of Homeland Security for further investigation if there is a matching name.

A few days ago, I blogged about a news article that revealed that 30,000 people are wrongly flagged as “matches” on the list.

So applying my very amateur mathematics skills, that means of the 80,000 names on the list, possibly about 30,000 of them (37.5%) match those of an innocent traveler.

Now, I bet that there are repeats, so several of the 30,000 could have the same name. If John Smith is one of the names on the list, it could account for a number of innocent travelers being flagged. Still, these numbers strike me as quite alarming. Something is seriously wrong. Is this really a competent way to go about airline security? What, precisely, gets a name on the list? Why are these lists so bad that they capture so many innocent people?

I guess the DHS is no Santa Claus.

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Hat tip: Privacy.org

### 3 Responses

1. ac says:

A healthy false positive rate is expected even with a very high quality list, given the number of travelers, the frequency of actual threats, and the nonuniqueness of names. The odds are stacked against the scheme. Biometrics have some prospect of reducing the number of false positives.