27 October 2008

More on Labour's Data Delusion

And so it goes on:

Every police force in the UK is to be equipped with mobile fingerprint scanners - handheld devices that allow police to carry out identity checks on people in the street.

The new technology, which ultimately may be able to receive pictures of suspects, is likely to be in widespread use within 18 months. Tens of thousands of sets - as compact as BlackBerry smartphones - are expected to be distributed.

The police claim the scheme, called Project Midas, will transform the speed of criminal investigations. A similar, heavier machine has been tested during limited trials with motorway patrols.

To address fears about mass surveillance and random searches, the police insist fingerprints taken by the scanners will not be stored or added to databases.

Yeah, pull the other one. The point is, given the current government's mentality that more is better, it is inevitable that these prints will be added. The irony is, this will actually make the system *less* useful.

To see why, consider what happens if there is a 1 in 100,000,000 chance of false positives using these new units. Suppose there are 1,000,000 fingerprints on the database: that means after 100 checks, there is likely to be a false match - bad enough. But now consider what happens when all these other fingerprints, obtained at random, are added, and the database increases to 10,000,000: a false positive will be obtained after every *10* checks on average. In other words, the more prints there are on the database, the worse the false positive rate becomes because of the unavoidable errors in biometrics.

This back of the envelope calculation also shows the way forward for biometric checks - of all kinds, since they are all subject to the same scaling problem. The government should aim to *reduce* the number of files it holds, but ensure that they are the ones that they are most interested in/concerned about. In other words, try to cut the database down to 100,000, say, but make sure they are *right* 100,000, not just random members of the public.

It's clear that the reason for Labour's data delusion is that it doesn't understood the technology that it is seeking to apply. In particular, it doesn't understand that the error rate sets a limit on the useful size of such databases. Super-duper databases are simply super stupid.


Anonymous said...

According to this: http://www.bioconsulting.com/bio.htm : single finger prints could be as bad as 1:500. Obviously, 2 prints decreases the error rate. It just makes CSI look even more foolish and I think this is where most MPs seem to get their science from.

Glyn Moody said...

Thanks for that. That's pretty incredible though: I assumed things were many orders of magnitude better...

I wonder if the system is set up for multiple prints from the same person, to be tested together.

Dr. Roy Schestowitz said...

Let's call it "fingerprint theatre". It makes you feel safe. Sci-fi stuff all ova' the place!

Glyn Moody said...

Has a nice ring to it....