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> Millimeter-wave machines at airports today are totally and completely useless. Germany's transportation administration reported a 54% false positive rate for

by eis 7y ago

> Millimeter-wave machines at airports today are totally and completely useless. Germany's transportation administration reported a 54% false positive rate for these pieces of rubbish. You are better off randomly searching people by flipping a coin. Edit: note that it seems I had a wrong understanding of the term false positive rate, ignore this comment. Statistics doesn't work like that. The false positive rate is pretty meaningless in this context. It only determines how much useless manual work is performed after the machine flags you incorrectly. You should look at the false negative rate in order to determine how much of a security plus they bring. That being said, I think the whole airport theater is ridicolous. If terrorists wanted to kill people, they literally have thousands of alternative ways to achieve that.

cookingrobot 7y ago
In this context of using them in public spaces it’s the false positive that matters most. The complaint is that the machines basically always alarm, which means the only thing they can be used for is making up a bogus excuse to manually search / harass someone based on no real suspicion.
- eis 7y ago
  But they don't always alarm according to the number that was presented. It alarms twice as many times as it should. That's not good and I certainly wouldn't want these in public spaces. But you can't just look at the false positive rate and how much more work and unpleasant/unnecessary searches they cause. You have to take into account the false negative rate to get a complete picture. Manufacturers and the people who want these machines will always err on the side of too many false positives than too many false negatives. Again, I personally think that these machines have no place in public spaces, no matter their hit/miss-rate.
  - Dylan16807 7y ago
    > It alarms twice as many times as it should. That's not what a false positive rate is. It alarms on half of everyone that goes through. It's utter garbage as a first-line test.
    - eis 7y ago
      I think this is a misunderstanding. From Wikipedia [1]: > A false positive error, or in short a false positive, commonly called a "false alarm", is a result that indicates a given condition exists, when it does not. So a 50% false positive means also that in 50% of alarms the condition was actually true. What you mean is a 50% alarm/trigger rate. Which, depending on how many people do have something on them that should trigger the alarm, would result in a far far higher false positive rate. 1: https://en.wikipedia.org/wiki/False_positives_and_false_negatives https://en.wikipedia.org/wiki/False_positives_and_false_nega...
      - Dylan16807 7y ago
        > What you mean is a 50% alarm/trigger rate. No I don't. It's just that the true positive rate is close enough to zero that both false positive and alarm rate are roughly the same number. Nevertheless you're still not understanding "false positive" correctly. If you correctly pick 5 out of 100 true positives without any flaws, and also have a 54% false positive rate, you're grabbing 51 false positives, and >90% of your picks were incorrect. And I'm pretty sure the true positive rate is well under 5% to start with, which just makes it worse. "In Germany, the false positive rate was 54 percent, meaning that every other person who went through the scanner had to undergo at least a limited pat-down that found nothing."
      - IanCal 7y ago
        This is wrong. Even your quote shows this. A false positive rate is how often it triggers when the true result is false. > A false positive error, or in short a false positive, commonly called a "false alarm", is a result that indicates a given condition exists, when it does not. So 50% false positive rate means 50% of people who should not be flagged are flagged. https://en.wikipedia.org/wiki/False_positive_rate https://en.wikipedia.org/wiki/False_positive_rate
  - atoav 7y ago
    It is quite definitly true that every second person needs to be patted down without a reason, purely on my personal experience as a frequent flyer
lazyasciiart 7y ago
Not quite true. A high false positive rate leads the people running the machines to stop reacting seriously to alerts, which means that they don’t do the manual checks with as much care. This is even more of an issue when everyone in line knows they are bullshit and has no respect for the people running them.
- eis 7y ago
  A false positive rate of close to 50% means that every second alert indeed pointed at something real. That should not cause the staff to get unmotivated. Again, without the false negative rate we can't judge if they are complete bullshit or not. If it were a 90% false positive rate then sure, that would clearly have the effects you outlined. I don't think at around 50% that's the case yet.
  - Dylan16807 7y ago
    > A false positive rate of close to 50% means that every second alert indeed pointed at something real. No it doesn't.
    - eis 7y ago
      Please see my other comment which references the definition of false positive rate because I think your understanding of the term is wrong. You have a 50% alarm/trigger rate in mind. And please try to reply with a bit more substance than "No".
      - Dylan16807 7y ago
        To quote an article on the subject: "meaning that every other person who went through the scanner had to undergo at least a limited pat-down that found nothing" > And please try to reply with a bit more substance than "No". Eh. I was hoping you'd just delete the comment rather than have two parallel arguments.
  - thomasahle 7y ago
    > The false positive rate is calculated as the ratio between the number of negative events wrongly categorized as positive (false positives) and the total number of actual negative events (regardless of classification). https://en.m.wikipedia.org/wiki/False_positive_rate https://en.m.wikipedia.org/wiki/False_positive_rate 54% FPR means half of all people who aren't trying to bring anything illegal onto the plane gets stopped. Since basically nobody are actually trying to do this, that also means that more than half of all people going through gets stopped. The ratio of true positives to positives must thus also be vanishingly small.
deleted 7y ago
[deleted]
bastardoperator 7y ago
This is what they do in Mexico when entering the country from the perspective of flipping a coin. I took my vacation in Maya Riveria and upon entering the country they have a box with a button. You push the button and it lights up green or red. Green means you go, red means you have some additional security checks.

by eis 7y ago

cookingrobot 7y ago

In this context of using them in public spaces it’s the false positive that matters most. The complaint is that the machines basically always alarm, which means the only thing they can be used for is making up a bogus excuse to manually search / harass someone based on no real suspicion.

eis 7y ago
But they don't always alarm according to the number that was presented. It alarms twice as many times as it should. That's not good and I certainly wouldn't want these in public spaces. But you can't just look at the false positive rate and how much more work and unpleasant/unnecessary searches they cause. You have to take into account the false negative rate to get a complete picture. Manufacturers and the people who want these machines will always err on the side of too many false positives than too many false negatives. Again, I personally think that these machines have no place in public spaces, no matter their hit/miss-rate.
- Dylan16807 7y ago
  > It alarms twice as many times as it should. That's not what a false positive rate is. It alarms on half of everyone that goes through. It's utter garbage as a first-line test.
  - eis 7y ago
    I think this is a misunderstanding. From Wikipedia [1]: > A false positive error, or in short a false positive, commonly called a "false alarm", is a result that indicates a given condition exists, when it does not. So a 50% false positive means also that in 50% of alarms the condition was actually true. What you mean is a 50% alarm/trigger rate. Which, depending on how many people do have something on them that should trigger the alarm, would result in a far far higher false positive rate. 1: https://en.wikipedia.org/wiki/False_positives_and_false_negatives https://en.wikipedia.org/wiki/False_positives_and_false_nega...
    - Dylan16807 7y ago
      > What you mean is a 50% alarm/trigger rate. No I don't. It's just that the true positive rate is close enough to zero that both false positive and alarm rate are roughly the same number. Nevertheless you're still not understanding "false positive" correctly. If you correctly pick 5 out of 100 true positives without any flaws, and also have a 54% false positive rate, you're grabbing 51 false positives, and >90% of your picks were incorrect. And I'm pretty sure the true positive rate is well under 5% to start with, which just makes it worse. "In Germany, the false positive rate was 54 percent, meaning that every other person who went through the scanner had to undergo at least a limited pat-down that found nothing."
    - IanCal 7y ago
      This is wrong. Even your quote shows this. A false positive rate is how often it triggers when the true result is false. > A false positive error, or in short a false positive, commonly called a "false alarm", is a result that indicates a given condition exists, when it does not. So 50% false positive rate means 50% of people who should not be flagged are flagged. https://en.wikipedia.org/wiki/False_positive_rate https://en.wikipedia.org/wiki/False_positive_rate
- atoav 7y ago
  It is quite definitly true that every second person needs to be patted down without a reason, purely on my personal experience as a frequent flyer

lazyasciiart 7y ago

Not quite true. A high false positive rate leads the people running the machines to stop reacting seriously to alerts, which means that they don’t do the manual checks with as much care. This is even more of an issue when everyone in line knows they are bullshit and has no respect for the people running them.

eis 7y ago
A false positive rate of close to 50% means that every second alert indeed pointed at something real. That should not cause the staff to get unmotivated. Again, without the false negative rate we can't judge if they are complete bullshit or not. If it were a 90% false positive rate then sure, that would clearly have the effects you outlined. I don't think at around 50% that's the case yet.
- Dylan16807 7y ago
  > A false positive rate of close to 50% means that every second alert indeed pointed at something real. No it doesn't.
  - eis 7y ago
    Please see my other comment which references the definition of false positive rate because I think your understanding of the term is wrong. You have a 50% alarm/trigger rate in mind. And please try to reply with a bit more substance than "No".
    - Dylan16807 7y ago
      To quote an article on the subject: "meaning that every other person who went through the scanner had to undergo at least a limited pat-down that found nothing" > And please try to reply with a bit more substance than "No". Eh. I was hoping you'd just delete the comment rather than have two parallel arguments.
- thomasahle 7y ago
  > The false positive rate is calculated as the ratio between the number of negative events wrongly categorized as positive (false positives) and the total number of actual negative events (regardless of classification). https://en.m.wikipedia.org/wiki/False_positive_rate https://en.m.wikipedia.org/wiki/False_positive_rate 54% FPR means half of all people who aren't trying to bring anything illegal onto the plane gets stopped. Since basically nobody are actually trying to do this, that also means that more than half of all people going through gets stopped. The ratio of true positives to positives must thus also be vanishingly small.

deleted 7y ago

[deleted]

bastardoperator 7y ago

This is what they do in Mexico when entering the country from the perspective of flipping a coin. I took my vacation in Maya Riveria and upon entering the country they have a box with a button. You push the button and it lights up green or red. Green means you go, red means you have some additional security checks.