Thursday, 27 June 2013

Why Mass Surveillance Does Not Work

by Dirk Helbing (ETH Zurich,

These days, it is often claimed that we need massive surveillance to ensure a high level of security. While the idea sounds plausible, I will explain, why this approach cannot work well, even when secret services have the very best intentions, and their sensitive knowledge would not be misused. This is a matter of statistics - no method is perfect.
For the sake of illustration, let us assume there are 2000 terrorists in a country with 200 Mio. inhabitants. Moreover, let us assume that the secret service manages to identify terrorists with an amazing 99% accuracy. Then, there are 1% false negatives (type II error), which means that 20 terrorists are not detected, while 1980 will be caught. The actual numbers are much smaller. It has been declared that 50 terror acts were prevented in about 12 years, while a few terrorist attacks could not be stopped (although the terrorists were often listed as suspects).
It is also important to ask, how many false positives ("false alarms") do we have? If the type I error is just 1 out of 10,000, there will be 20,000 wrong suspects, if it is 1 permille, there will be 200,000 wrong suspects, and if it is 1 percent, it will be 2 million false suspects. Recent figures I have heard of on TV spoke of 8 Million suspects in the US in 1996, which would mean about a 4 percent error rate. If these figures are correct, this would mean that for every terrorist, 4000 times as many innocent citizens would be wrongly categorized as (potential) terrorists.
Hence, large-scale surveillance is not an effective means of fighting terrorism. It rather tends to restrict the freedom rights of millions of innocent citizens. It is not reasonable to apply surveillance to the whole population, for the same reasons, why it is not sensible to make a certain medical test with everybody. There would be millions of false positives, i.e. millions of people who would be wrongly treated, with negative side effects on their health. For this reason, patients are tested for diseases only if they show worrying symptoms.
In the very same way, it creates more harm than benefit, if everybody is being screened for being a potential future terrorist. This will cause unjustified discrimination and harmful self-censorship at times, where unconventional, new ideas are needed more than ever. It will impair the ability of our society to innovate and adapt, thereby promoting instability. Thus, it is time to pursue a different approach, namely to identify the social, economic and political factors that promote crime and terrorism, and to change these factors. Just 2 decades back, we saw comparatively little security problems in most modern societies. Overall, people tolerated each other and coexisted peacefully, without massive surveillance and policing. We were living in a free and happy world, where people of different cultural backgrounds respected each other and did not have to live in fear. Can we have this time back, please?


Type I and type II errors, see


  1. Combating subservience and protecting your right to privacy should be a huge priority. There are many tools,techniques and methods once can employ in order to ensure that no one is violating your rights. Counter surveillance is a big part of any effort to protect yourself using tools such as a spy listening device or CCTV cameras.

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