Report: No Fly - Homeland Security

No-Fly Report
DHS Privacy Office
April 27, 2006
The Privacy Office believes that the current TSC standards for No-fly and Selectee lists
are sufficiently narrow, while still broad enough to be effective for screening purposes.
In reaching this conclusion, the Privacy Office primarily examined the standards from a
privacy and fair information principles perspective rather than from a law enforcement
perspective because the law enforcement decision about the risk to aviation security
posed by an individual or his associates is for other offices to make. The more the lists
expand beyond individuals who are believed to pose a potential threat to civil aviation,
however, the greater the likelihood that some individuals, whose relationship to aviation
security threats is highly speculative, will be subjected to additional screening or
prevented from traveling. If there is no relationship between the threat to civil aviation
and the placement of an individual on a list that bars the individual’s ability to travel,
there may be an insufficient predicate reason to interfere with travel.
C. Matching Errors
All systems for matching names against watch lists are prone to errors. There is a
potential for two types of errors that result from improper matching between an
individual and a record on a watch list. A “false positive” occurs when the system
signals that someone is on a watch list when the individual is not on the list. A “false
negative” occurs when the system does not signal that an individual is on a watch list
when the individual is actually on the list. In the context of terrorism screening, false
positives give rise to privacy and civil liberties concerns because they can result in a
range of consequences for innocent individuals. False negatives, on the other hand, give
rise to security concerns because they allow known or suspected terrorists to slip through
the detection system.
System designers must perform a trade-off between false positives and false negatives
generated by a system—as one type of error decreases, the likelihood of the other type
tends to increase, because a correlation tends to exist between these two types of errors.
In other words, if a system is designed to minimize false negatives, it will produce a
larger number of false positives, and vice versa. In terrorist screening systems, false
negatives are potentially very costly in terms of lives that might be lost and in terms of
economic damage resulting from acts of terrorism. However, there are very few
individuals on watch lists compared to the number of individuals who are matched
against these lists, so a system that is very sensitive to false negatives has the potential to
produce a large number of false positives. 32
32 For example, let us say that a system is 99.9 percent effective in doing its matches. With approximately
1.8 million passengers flying in the United States daily, the 99.9 percent accuracy rate would produce 1,800
errors per day.
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