All I want for Christmas is the presumption of innocence

by Matthew Gast

Related link: http://www.interesting-people.org/archives/interesting-people/200212/msg00061.ht…




Last week, Andy Oram
wrote
about a recent INS directive for men from twenty Muslim or Arab countries to report for screening. The
New York Times article
he links notes that "all but 20 of the hundreds" of detainees were released. Defining "potential terrorist" as "male of Arab descent or Muslim heritage" is so antithetical to civil liberties that a round-up is unacceptable. Even if we were willing to throw our civil liberties out the window (which, for the record, I am not), mass screening is a costly and ineffective approach.




The official used as the source for the Times story declined to state how many people were processed. Naturally, that made me curious. Although I am not a serious statistician, "all but 20" has much less relevance without knowing what it is measured in relation to. Did the INS harass thousands of people, most of whom were undoubtedly honest, to find the 20 suspects worthy of further investigation? Probably, given the broad language being used to describe the effort elsewhere. (I first heard about it on KQED's
California Report
on December 18. There was a follow-up story December 23 reporting on related protests.)




While pondering the difficulties in rounding up such a broad group of people, and wondering whether or not they were treated as humanely as the INS insisted, I came across the linked message on the Interesting People mailing list. The author, a computer science professor at UT-Austin, has an incisive analysis of the statistical failures of a broad screening approach, even if supervised by humans. His argument is constructed by analogy to screening for a rare disease in a medical laboratory. No screening process will identify everybody who has the condition, and substantial numbers of unaffected people are misidentified along the way.




Moreover, in many lab settings, you can correctly assume that you have all the samples. In other cases, extremely strong privacy protections can help people feel less wary about the privacy implications of tests. In the case of an INS order to report for a background check, it is safe to assume that people with questionable backgrounds will attempt to avoid reporting, thus skewing the population of those screened far more in favor of the innocent. Such a tilt will tend to make the cost/benefit calculation worse by increasing the costs to innocent people while decreasing the small benefit that results from hysterical mass screening.




The presumpution of innocence has long served as a check on intrusive governments, and it is one of the pillars of our criminal justice system. Demagogues often attempt to weaken it by presenting a false dichotomy between the abstract concept of rights and a tangible feeling of security, often conjuring up criminal demons to frighten us into choosing the latter. Screening programs targeting broadly shared characteristics must be resisted on the grounds that they are antithetical to this country's founding principles. Furthermore, as a practical matter, they are almost totally ineffective at anything other than wasting money while proving our hypocrisy.




Speaking of hysterical mass screening and wasting money, the TSA apparently has decided to follow the lead of whatever bonehead at the INS ordered the round up. The TSA
is
advising fliers to leave luggage unlocked
to make supplmental baggage screening easier. The same mathematical analysis in searching for rare conditions almost certainly applies, given that most airline passengers are not terrorists. I would guess that most checked bags are not selected for a supplemental hand-search, and of those that are, most are not problematic. Meanwhile, there are definite costs associated with leaving checked luggage unlocked, especially at a time of year when people are likely to be transporting valuables. Fortunately, the TSA is looking out for me and is willing to trade the security of my possessions for my safety.



3 Comments

anonymous2
2002-12-24 14:36:36
Fine, I agree. So -- what _should_ we do???
I'm not much of a statistician, either, but I
understand the Bayesian statistics enough to
agree with you. Broad screening for a rare condition
will lead to a large number of false positives, while
providing no guarantee that all the rare conditions
are caught. (Unless, of course, the test is perfect :-)


But here's the part I'm missing. What _should_ we do? Broad screening is ineffective, but what
would work better? Broad screening produces bad side effects, but what better method would produce fewer side effects?


Remember, I agree with you. But are you arguing
that we should do nothing? That would be a political looser. Just how much power and money
should be thrown at the FBI to be "effective"
in lieu of broad screening?


And remember, "broad screening" includes
not just rounding up the usual suspects,
but also screening of airline passengers,
screening of web pages or email for
secret messages, screening of people for rare diseases that indicate biowarfare, and so on.


Bob Goldstein

anonymous2
2002-12-26 03:37:03
Why do anything?
It is the perception of bigotry and self-righteousness which has caused so much distrust and hatred toward the US and the UK (my country) throughout the World. This kind of behaviour will cause even more anger and sadly also achieve nothing.


What to do? Use an intelligent and balanced approach toward fighting the terror paralysing all the decision making. Afghanistan was the focus - yet what have we really resolved there? Civil liberties are improved in Afghanistan this evening but the underlying problems still persist and we have walked away - again. Devestate a system and run. How many decades until it's a problem again?


Now imagine the roles altered - the boot on the other foot and your entire civilistaion and social structure routed - decade after decade. We are so short sited - and it is at our own cost as much as other - in the long term.


Military action will only be useful if it actually achieves the ends the proclaims. What if there are dirty bombs and other w.o.m.d. - and what if Iraq is not the main cause for concern? Maybe N. Korea or ex-Soviet countries?


Increasingly I distrust the judgements being made and if an attack does happen in our soil -then it's me and my kids (and you/your's) who suffer - and I will vent my fury at the lies and deceit of our leaders then, too. If I am still around. Damn sure they stand a better chance of survival than me.


How many of you genuinely believe the motivation for attack on Iraq is motivated purely upon the politically inspired fears we currently hear? I stopped believing the spin long ago. So when will they come up with some real, new and effective solutions to the problem, instead of creating even more hatred - which is the fuel which set this all off.

andyo
2002-12-27 11:16:55
Yet more cause for alarm
Thanks, Matthew, for refering back to my weblog. Here's another bold expose, this one from the Washington Post:


http://www.washingtonpost.com/wp-dyn/articles/A37943-2002Dec25.html
U.S. Decries Abuse but Defends Interrogations


Some teaser quotes from unnamed U.S. officials:


"If you don't violate someone's human rights some of the
time, you probably aren't doing your job,"


"We don't kick the [expletive] out of them. We send them
to other countries so they can kick the [expletive] out
of them."


An editorial about it in the Post:


http://www.washingtonpost.com/wp-dyn/articles/A42024-2002Dec26.html
Torture Is Not an Option


When you think of the victims of this sanctioned activity, remember that objective observers have warned that several dozen of the hundreds of people taken to Guantanamo Bay are probably innocent bystanders caught up by mistake or by malice. If such a high percentage of Guantanamo Bay prisoners (being held with no regard for any legal norms, domestic or foreign) are probably innocent, how many of those being held in Afghanistan probably are too?


I vaguely remember a couple years ago that Congress closed a loophole and told U.S. courts they couldn't accept evidence from other countries that was obtained by means that would be considered unconstitutional in the U.S., even if those means were tolerated in the country where they were used. Well, that was before the apocalypse (9/11/2001).