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This is a weak argument from Schneier. Most of his concerns (false positives, false negatives) also apply to contact tracing done by humans, which he advocates

by feral 6y ago

This is a weak argument from Schneier. Most of his concerns (false positives, false negatives) also apply to contact tracing done by humans, which he advocates at the end of his article. If a medical professional interviews you about your contacts, you have to remember who they were. If you forget someone, or didn't know their name, that's a false negative. Someone you report you had coffee with, but who doesn't get the disease, is a false positive. Apps have different limitations, and need adoption to be useful, and that's a problem societies will have to consider. There's also legit privacy concerns. But the very broad argument made in that post is silly. You just don't need to stop every transmission to stop the disease. Even stopping 70%, via a range of measures, is about enough. You can tolerate some errors.

mellow2020 6y ago
The dichotomy isn't between the app or a medical professional guessing, based on contacts, whether someone might be infected and whether they should self-quarantine. The dichotomy is between guessing infection based on contacts and testing for infection.
- pimterry 6y ago
  There isn't a dichotomy. We can use all these techniques. Testing is great of course, but given that you can't test everybody every day, testing is more effective when you can test the right people. If we can trace contacts, we can prioritize testing of people who've had a possible contact recently, and thereby find and quarantine infectious people faster.
  - mellow2020 6y ago
    > There isn't a dichotomy. I simply meant that this "without ubiquitous, cheap, fast, and accurate testing, you can't confirm the app's diagnosis. So the alert is useless." was turned into medical professionals asking someone about contacts, a la "Someone you report you had coffee with, but who doesn't get the disease, is a false positive" to show that getting asked about contacts by medical professionals isn't better than a contact tracing app, which is a straw man, i.e. Schneier didn't ask for medical professionals to ask those questions, he said those questions are useless without tests.
    - nshepperd 6y ago
      He did ask for that, at the end of his post: > It has nothing to do with privacy concerns. The idea that contact tracing can be done with an app, and not human health professionals, is just plain dumb. Human health professionals doing contact tracing means exactly that.
      - mellow2020 6y ago
        In context, given all he wrote before, it's obvious that he means testing, not asking questions about who someone had coffee with.
        sanderjd 6y ago
        No not at all, in that sentence he is talking about human health professionals doing contact tracing rather than apps. Which is why the thread-starter is right that his argument here is silly. It would be better for him to be clear-eyed that he is biased against technological contact-tracing solutions in favor of human ones, because of his privacy concerns. That is a totally reasonable position! What is not reasonable is arguing against using technology for contact tracing because it has false-positive and false-negative problems; it's true that it does, but all contact tracing solutions are probabilistic in this way.
- feral 6y ago
  You may be misunderstanding the purpose of contact tracing? It's not to guess whether a patient you have is infected. It is to find the people that patient has infected before those infect more people. If things are being run properly: 1. Someone shows up with the disease. (Tests positive, or clinical.) 2. You find their contacts, either by app or interview or both. 3. You tell those contacts to quarantine, hopefully before they've become infectious, breaking onward spread. 4. If they test negative and don't display symptoms, they stop quarantine. Unless you mean to test everyone every day? Sounds good, but then you need way more tests than countries have been able to make so far, and they have to be very sensitive and specific too, even before someone is infectious.
  - yummybear 6y ago
    Regarding 3) - should they quarantine regardless or just if the get ill?
    - enitihas 6y ago
      They should quarantine regardless, since asymptomatic people are also spreaders. Ill people sre anyways getting quarantined even without any tracing.
    - chosenbreed37 6y ago
      > Regarding 3) - should they quarantine regardless or just if the get ill? I guess they have to quarantine. Not only them but anybody else that came into contact with and so and so forth :-)
    - feral 6y ago
      Probably. I would say that depends on the overall strategy. If pre-symptomatic people infecting others is a big issue, then it's probably worth the cost of quarantining folks who display no symptoms until you are sure they aren't sick. Obviously that means you quarantine a lot of people who don't later get sick. That sounds draconian, but its a lot better than lockdowns.
    - fragmede 6y ago
eplanit 6y ago
"You just don't need to stop every transmission to stop the disease. Even stopping 70%, via a range of measures, is about enough. You can tolerate some errors." Please explain this to Gavin Newsom.
- joshuamorton 6y ago
  The measures we have in place in CA do stop 50-70% of transmissions. The challenge is relaxing some of those while keeping transmission at the level that it is.
rovolo 6y ago
You're right that human contact-tracing also has false positives/negatives. I think a better question is how does the error rate compare? The worry is that automated exposure tracking will pick up many more false positives than humans will because it's hard to judge how likely a transmission occurred. A phone doesn't know if there are barriers between people (walls, PPE). The downside to a higher false positive/negative rate is that you'll create more false alarms. At some point, people will start ignoring false alarms. With phone tracking, you are probably trading off many more false positives for a couple fewer false negatives. It's unclear whether this tradeoff is worth it because we don't know how people will respond long-run to automated exposure notifications.
alerighi 6y ago
The concern is that if the app just gives you a ton of alerts, because maybe you encountered someone in the street with the virus but it's unlikely that you have been infected, people will simply ignore that alterts (or simply uninstall the apps), because you know, who wants to be quaranteened for 2 weeks because there is the remote possibility of having the virus? Maybe they do that on the first alert, at the second one they says who cares, I need to carry on with my business. One could argue that who recieves the notification should not quaraneen but get tested immediately, well we know that we don't have the resources to test all these people, in my country they don't even test people with symptoms if they are not severe enought, let alone test someone because an app says so. Also an app could give a false sense of security, that is particularly bad. The app only can say if you got in contact with a positive that also had the app, that quite frankly will not be common, first because not everyone has a compatible phone (in my country only 70% of people have a smartphone, also you need an updated phone to install the app, on iOS the APIs that will make it work are just being released in the next iOS beta), then the app will be voluntary and thus not everyone with a compatible phone will install it, for privacy concerns or other reaons (like not being forced to quaranteen for the remote possibility of having been infected). Thus I predict that maybe we are lucky if 20% of people have the app (that is compatible to what happened in the countries that already adopted it). And that is a percentage that make the app itself useless, because you have too few data.
- majewsky 6y ago
  > if the app just gives you a ton of alerts, because maybe you encountered someone in the street with the virus If I'm not mistaken, the protocol as currently defined by Apple and Google only flags an exposure if you have seen at least two different beacon payloads from the same issuer. The payload changes every 5 minutes, so you would usually not receive an exposure notification when an infected person just passes by you on the street. You might see one of their beacons, but probably not two, and most probably not two beacons with different payloads.

by feral 6y ago

mellow2020 6y ago

The dichotomy isn't between the app or a medical professional guessing, based on contacts, whether someone might be infected and whether they should self-quarantine. The dichotomy is between guessing infection based on contacts and testing for infection.

pimterry 6y ago
There isn't a dichotomy. We can use all these techniques. Testing is great of course, but given that you can't test everybody every day, testing is more effective when you can test the right people. If we can trace contacts, we can prioritize testing of people who've had a possible contact recently, and thereby find and quarantine infectious people faster.
- mellow2020 6y ago
  > There isn't a dichotomy. I simply meant that this "without ubiquitous, cheap, fast, and accurate testing, you can't confirm the app's diagnosis. So the alert is useless." was turned into medical professionals asking someone about contacts, a la "Someone you report you had coffee with, but who doesn't get the disease, is a false positive" to show that getting asked about contacts by medical professionals isn't better than a contact tracing app, which is a straw man, i.e. Schneier didn't ask for medical professionals to ask those questions, he said those questions are useless without tests.
  - nshepperd 6y ago
    He did ask for that, at the end of his post: > It has nothing to do with privacy concerns. The idea that contact tracing can be done with an app, and not human health professionals, is just plain dumb. Human health professionals doing contact tracing means exactly that.
    - mellow2020 6y ago
      In context, given all he wrote before, it's obvious that he means testing, not asking questions about who someone had coffee with.
      - sanderjd 6y ago
        No not at all, in that sentence he is talking about human health professionals doing contact tracing rather than apps. Which is why the thread-starter is right that his argument here is silly. It would be better for him to be clear-eyed that he is biased against technological contact-tracing solutions in favor of human ones, because of his privacy concerns. That is a totally reasonable position! What is not reasonable is arguing against using technology for contact tracing because it has false-positive and false-negative problems; it's true that it does, but all contact tracing solutions are probabilistic in this way.
feral 6y ago
You may be misunderstanding the purpose of contact tracing? It's not to guess whether a patient you have is infected. It is to find the people that patient has infected before those infect more people. If things are being run properly: 1. Someone shows up with the disease. (Tests positive, or clinical.) 2. You find their contacts, either by app or interview or both. 3. You tell those contacts to quarantine, hopefully before they've become infectious, breaking onward spread. 4. If they test negative and don't display symptoms, they stop quarantine. Unless you mean to test everyone every day? Sounds good, but then you need way more tests than countries have been able to make so far, and they have to be very sensitive and specific too, even before someone is infectious.
- yummybear 6y ago
  Regarding 3) - should they quarantine regardless or just if the get ill?
  - enitihas 6y ago
    They should quarantine regardless, since asymptomatic people are also spreaders. Ill people sre anyways getting quarantined even without any tracing.
  - chosenbreed37 6y ago
    > Regarding 3) - should they quarantine regardless or just if the get ill? I guess they have to quarantine. Not only them but anybody else that came into contact with and so and so forth :-)
  - feral 6y ago
    Probably. I would say that depends on the overall strategy. If pre-symptomatic people infecting others is a big issue, then it's probably worth the cost of quarantining folks who display no symptoms until you are sure they aren't sick. Obviously that means you quarantine a lot of people who don't later get sick. That sounds draconian, but its a lot better than lockdowns.
  - fragmede 6y ago

eplanit 6y ago

"You just don't need to stop every transmission to stop the disease. Even stopping 70%, via a range of measures, is about enough. You can tolerate some errors." Please explain this to Gavin Newsom.

joshuamorton 6y ago
The measures we have in place in CA do stop 50-70% of transmissions. The challenge is relaxing some of those while keeping transmission at the level that it is.

rovolo 6y ago

You're right that human contact-tracing also has false positives/negatives. I think a better question is how does the error rate compare? The worry is that automated exposure tracking will pick up many more false positives than humans will because it's hard to judge how likely a transmission occurred. A phone doesn't know if there are barriers between people (walls, PPE). The downside to a higher false positive/negative rate is that you'll create more false alarms. At some point, people will start ignoring false alarms. With phone tracking, you are probably trading off many more false positives for a couple fewer false negatives. It's unclear whether this tradeoff is worth it because we don't know how people will respond long-run to automated exposure notifications.

alerighi 6y ago

The concern is that if the app just gives you a ton of alerts, because maybe you encountered someone in the street with the virus but it's unlikely that you have been infected, people will simply ignore that alterts (or simply uninstall the apps), because you know, who wants to be quaranteened for 2 weeks because there is the remote possibility of having the virus? Maybe they do that on the first alert, at the second one they says who cares, I need to carry on with my business. One could argue that who recieves the notification should not quaraneen but get tested immediately, well we know that we don't have the resources to test all these people, in my country they don't even test people with symptoms if they are not severe enought, let alone test someone because an app says so. Also an app could give a false sense of security, that is particularly bad. The app only can say if you got in contact with a positive that also had the app, that quite frankly will not be common, first because not everyone has a compatible phone (in my country only 70% of people have a smartphone, also you need an updated phone to install the app, on iOS the APIs that will make it work are just being released in the next iOS beta), then the app will be voluntary and thus not everyone with a compatible phone will install it, for privacy concerns or other reaons (like not being forced to quaranteen for the remote possibility of having been infected). Thus I predict that maybe we are lucky if 20% of people have the app (that is compatible to what happened in the countries that already adopted it). And that is a percentage that make the app itself useless, because you have too few data.

majewsky 6y ago
> if the app just gives you a ton of alerts, because maybe you encountered someone in the street with the virus If I'm not mistaken, the protocol as currently defined by Apple and Google only flags an exposure if you have seen at least two different beacon payloads from the same issuer. The payload changes every 5 minutes, so you would usually not receive an exposure notification when an infected person just passes by you on the street. You might see one of their beacons, but probably not two, and most probably not two beacons with different payloads.