4 ms·

> Police facial recognition cameras have been trialled at events such as football matches, festivals and parades... High-definition cameras detect all the faces

by jfasi 8y ago

> Police facial recognition cameras have been trialled at events such as football matches, festivals and parades... High-definition cameras detect all the faces in a crowd and compare them with existing police photographs, such as mugshots from previous arrests. > "When we first deployed and we were learning how to use it... some of the digital images we used weren't of sufficient quality," said Deputy Chief Constable Richard Lewis. "Because of the poor quality, it was identifying people wrongly. They weren't able to get the detail from the picture." > Information Commissioner Elizabeth Denham said the issue had become a "priority" for her office. When you roll out facial recognition technology at an event with ten thousand people and expect your magical facial recognition system to pick out just the bad guys, you quickly discover that even a system that's 99.99 percent accurate has a 63 percent change of giving you at least one false positive in that crowd. In reality these systems are probably closer to 95 percent accurate, in which case you're looking at vastly more false positives. Like hundreds per event. This is the exact same statement as "breast cancer screening is staggeringly inaccurate." Do you know why breast annual cancer screenings aren't recommended for women under 40? Because breast cancer is so rare in that population that the high false positive rate outweighs the benefit of early detection. The correct thing to do is only screen only if there is already a suspicion of cancer. Similarly, pervasive surveillance where you (statistically) consider everyone a possible criminal is a waste of time. Anyone who's ever taken a probability course will tell you that unless your facial recognition tech is fantastically accurate you'll waste all your police officers' valuable time sorting through false positives. This is not an image quality issue. It's not a data quality issue. It's not a deployment issue. It's a Bayesian statistics issue. Unless your tech has superhuman 99.999% accuracy, it doesn't matter how accurate your facial recognition is if you're looking for a needle in a haystack. I'm sure the facial recognition is just as wonderfully accurate as breast cancer screening, it's just being applied to a population with a stupidly rare prior. This is a statistics 101, freshman undergrad-level mistake, and frankly it makes me mad as hell that authorities are stupid enough to make it and boneheaded enough to endanger their entire population's civil liberties in the process. For more info, check Wikipedia's page on the aptly-named prosecutor's fallacy: https://en.wikipedia.org/wiki/Prosecutor%27s_fallacy https://en.wikipedia.org/wiki/Prosecutor%27s_fallacy

tzs 8y ago
The base rate fallacy [1] and the false positive paradox [2] seem to be much more on point for using face recognition for screening seem to be much more on point than the prosecutor's fallacy. [1] https://en.wikipedia.org/wiki/Base_rate_fallacy https://en.wikipedia.org/wiki/Base_rate_fallacy [2] https://en.wikipedia.org/wiki/False_positive_paradox https://en.wikipedia.org/wiki/False_positive_paradox
- thaumasiotes 8y ago
  What exactly are you trying to correct? Read your own link. https://en.wikipedia.org/wiki/False_positive_paradox https://en.wikipedia.org/wiki/False_positive_paradox says: > concluding that a positive test result probably indicates a positive subject, even though population incidence is below the false positive rate, is a "base rate fallacy". Whereas https://en.wikipedia.org/wiki/Prosecutor%27s_fallacy https://en.wikipedia.org/wiki/Prosecutor%27s_fallacy says: > At its heart, the fallacy involves assuming that the prior probability of a random match [i.e. the odds of a positive test result] is equal to the probability that the defendant is innocent [i.e. the odds of a positive subject]. For instance, if a perpetrator is known to have the same blood type as a defendant and 10% of the population share that blood type, then to argue on that basis alone that the probability of the defendant being guilty is 90% makes the prosecutor's fallacy Those are the same mistake. The prosecutor's fallacy is a base rate fallacy.
  - tzs 8y ago
    False positive paradox: "The false positive paradox is a statistical result where false positive tests are more probable than true positive tests, occurring when the overall population has a low incidence of a condition and the incidence rate is lower than the false positive rate" Prosecutor's fallacy: "The prosecutor's fallacy is a fallacy of statistical reasoning, typically used by the prosecution to argue for the guilt of a defendant during a criminal trial". The false positive paradox is a result. To get to a prosecutor's fallacy or base rate fallacy from it, you have to use the result in a way that involves certain fallacious reasoning. There's nothing necessarily wrong with using a screening test that the false positive paradox applies to, as long as you recognize its limitations. When you are looking for a needle in a haystack (which is typically when you hit the false positive paradox) it gives you a smaller haystack to search for the needle, but that can still be a big improvement over not using it as long as it has a low false negative rate.

by jfasi 8y ago

tzs 8y ago

The base rate fallacy [1] and the false positive paradox [2] seem to be much more on point for using face recognition for screening seem to be much more on point than the prosecutor's fallacy. [1] https://en.wikipedia.org/wiki/Base_rate_fallacy https://en.wikipedia.org/wiki/Base_rate_fallacy [2] https://en.wikipedia.org/wiki/False_positive_paradox https://en.wikipedia.org/wiki/False_positive_paradox

thaumasiotes 8y ago
What exactly are you trying to correct? Read your own link. https://en.wikipedia.org/wiki/False_positive_paradox https://en.wikipedia.org/wiki/False_positive_paradox says: > concluding that a positive test result probably indicates a positive subject, even though population incidence is below the false positive rate, is a "base rate fallacy". Whereas https://en.wikipedia.org/wiki/Prosecutor%27s_fallacy https://en.wikipedia.org/wiki/Prosecutor%27s_fallacy says: > At its heart, the fallacy involves assuming that the prior probability of a random match [i.e. the odds of a positive test result] is equal to the probability that the defendant is innocent [i.e. the odds of a positive subject]. For instance, if a perpetrator is known to have the same blood type as a defendant and 10% of the population share that blood type, then to argue on that basis alone that the probability of the defendant being guilty is 90% makes the prosecutor's fallacy Those are the same mistake. The prosecutor's fallacy is a base rate fallacy.
- tzs 8y ago
  False positive paradox: "The false positive paradox is a statistical result where false positive tests are more probable than true positive tests, occurring when the overall population has a low incidence of a condition and the incidence rate is lower than the false positive rate" Prosecutor's fallacy: "The prosecutor's fallacy is a fallacy of statistical reasoning, typically used by the prosecution to argue for the guilt of a defendant during a criminal trial". The false positive paradox is a result. To get to a prosecutor's fallacy or base rate fallacy from it, you have to use the result in a way that involves certain fallacious reasoning. There's nothing necessarily wrong with using a screening test that the false positive paradox applies to, as long as you recognize its limitations. When you are looking for a needle in a haystack (which is typically when you hit the false positive paradox) it gives you a smaller haystack to search for the needle, but that can still be a big improvement over not using it as long as it has a low false negative rate.