paranoid yet?

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The Politics of Paranoia and Intimidation

Why Does the NSA Engage in Mass Surveillance of Americans When It's

Statistically Impossible for Such Spying to Detect Terrorists?

By FLOYD RUDMIN

 

The Bush administration and the National Security Agency (NSA) have

been secretly monitoring the email messages and phone calls of all

Americans. They are doing this, they say, for our own good. To find

terrorists. Many people have criticized NSA's domestic spying as

unlawful invasion of privacy, as search without search warrant, as

abuse of power, as misuse of the NSA's resources, as unConstitutional,

as something the communists would do, something very unAmerican.

 

In addition, however, mass surveillance of an entire population cannot

find terrorists. It is a probabilistic impossibility. It cannot work.

 

What is the probability that people are terrorists given that NSA's

mass surveillance identifies them as terrorists? If the probability is

zero (p=0.00), then they certainly are not terrorists, and NSA was

wasting resources and damaging the lives of innocent citizens. If the

probability is one (p=1.00), then they definitely are terrorists, and

NSA has saved the day. If the probability is fifty-fifty (p=0.50), that

is the same as guessing the flip of a coin. The conditional probability

that people are terrorists given that the NSA surveillance system says

they are, that had better be very near to one (p_1.00) and very far

from zero (p=0.00).

 

The mathematics of conditional probability were figured out by the

Scottish logician Thomas Bayes. If you Google " Bayes' Theorem " , you

will get more than a million hits. Bayes' Theorem is taught in all

elementary statistics classes. Everyone at NSA certainly knows Bayes'

Theorem.

 

To know if mass surveillance will work, Bayes' theorem requires three

estimations:

 

1) The base-rate for terrorists, i.e. what proportion of the population

are terrorists.

 

2) The accuracy rate, i.e., the probability that real terrorists will

be identified by NSA;

 

3) The misidentification rate, i.e., the probability that innocent

citizens will be misidentified by NSA as terrorists.

 

No matter how sophisticated and super-duper are NSA's methods for

identifying terrorists, no matter how big and fast are NSA's computers,

NSA's accuracy rate will never be 100% and their misidentification rate

will never be 0%. That fact, plus the extremely low base-rate for

terrorists, means it is logically impossible for mass surveillance to

be an effective way to find terrorists.

 

I will not put Bayes' computational formula here. It is available in

all elementary statistics books and is on the web should any readers be

interested. But I will compute some conditional probabilities that

people are terrorists given that NSA's system of mass surveillance

identifies them to be terrorists.

 

The US Census shows that there are about 300 million people living in

the USA.

 

Suppose that there are 1,000 terrorists there as well, which is

probably a high estimate. The base-rate would be 1 terrorist per

300,000 people. In percentages, that is .00033% which is way less than

1%. Suppose that NSA surveillance has an accuracy rate of .40, which

means that 40% of real terrorists in the USA will be identified by

NSA's monitoring of everyone's email and phone calls. This is probably

a high estimate, considering that terrorists are doing their best to

avoid detection. There is no evidence thus far that NSA has been so

successful at finding terrorists. And suppose NSA's misidentification

rate is .0001, which means that .01% of innocent people will be

misidentified as terrorists, at least until they are investigated,

detained and interrogated. Note that .01% of the US population is

30,000 people. With these suppositions, then the probability that

people are terrorists given that NSA's system of surveillance

identifies them as terrorists is only p=0.0132, which is near zero,

very far from one. Ergo, NSA's surveillance system is useless for

finding terrorists.

 

Suppose that NSA's system is more accurate than .40, let's say, .70,

which means that 70% of terrorists in the USA will be found by mass

monitoring of phone calls and email messages. Then, by Bayes' Theorem,

the probability that a person is a terrorist if targeted by NSA is

still only p=0.0228, which is near zero, far from one, and useless.

 

Suppose that NSA's system is really, really, really good, really,

really good, with an accuracy rate of .90, and a misidentification rate

of .00001, which means that only 3,000 innocent people are

misidentified as terrorists. With these suppositions, then the

probability that people are terrorists given that NSA's system of

surveillance identifies them as terrorists is only p=0.2308, which is

far from one and well below flipping a coin. NSA's domestic monitoring

of everyone's email and phone calls is useless for finding terrorists.

 

NSA knows this. Bayes' Theorem is elementary common knowledge. So, why

does NSA spy on Americans knowing it's not possible to find terrorists

that way? Mass surveillance of the entire population is logically

sensible only if there is a higher base-rate. Higher base-rates arise

from two lines of thought, neither of them very nice:

 

1) McCarthy-type national paranoia;

 

2) political espionage.

 

The whole NSA domestic spying program will seem to work well, will seem

logical and possible, if you are paranoid. Instead of presuming there

are 1,000 terrorists in the USA, presume there are 1 million

terrorists. Americans have gone paranoid before, for example, during

the McCarthyism era of the 1950s. Imagining a million terrorists in

America puts the base-rate at .00333, and now the probability that a

person is a terrorist given that NSA's system identifies them is p=.99,

which is near certainty. But only if you are paranoid. If NSA's

surveillance requires a presumption of a million terrorists, and if in

fact there are only 100 or only 10, then a lot of innocent people are

going to be misidentified and confidently mislabeled as terrorists.

 

The ratio of real terrorists to innocent people in the prison camps of

Guantanamo, Abu Ghraib, and Kandahar shows that the US is paranoid and

is not bothered by mistaken identifications of innocent people. The

ratio of real terrorists to innocent people on Bush's no-fly lists

shows that the Bush administration is not bothered by mistaken

identifications of innocent Americans.

 

Also, mass surveillance of the entire population is logically plausible

if NSA's domestic spying is not looking for terrorists, but looking for

something else, something that is not so rare as terrorists. For

example, the May 19 Fox News opinion poll of 900 registered voters

found that 30% dislike the Bush administration so much they want him

impeached. If NSA were monitoring email and phone calls to identify

pro-impeachment people, and if the accuracy rate were .90 and the error

rate were .01, then the probability that people are pro-impeachment

given that NSA surveillance system identified them as such, would be

p=.98, which is coming close to certainty (p_1.00). Mass surveillance

by NSA of all Americans' phone calls and emails would be very effective

for domestic political intelligence.

 

But finding a few terrorists by mass surveillance of the phone calls

and email messages of 300 million Americans is mathematically

impossible, and NSA certainly knows that.

 

Floyd Rudmin is Professor of Social & Community Psychology at the

University of Tromsø in Norway. He can be reached at

frudmin

 

 

What's gonna happen when the buses don't run

and what's gonna happen when the, winter comes

what are you gonna do,

what are you gonna do

when the oil runs out?