8 ms·

I really question whether these apps will be effective. The limitation section https://github.com/corona-warn-app/cwa-documentation/blob/master/solution_archite

I really question whether these apps will be effective. The limitation section https://github.com/corona-warn-app/cwa-documentation/blob/master/solution_architecture.md#limitations https://github.com/corona-warn-app/cwa-documentation/blob/ma... of their architecture document shows that people in close proximity for a few minutes may not even get picked up. Anyone who has dealt with trying to work out distance from Bluetooth signal strength will know that it is virtually impossible once you factor in, the orientation of two devices (signal polarization), their locations (in a pocket, bag, case...) and the local environment (reflections and attenuation from walls, floors ceilings, furniture). Additionally, without knowing exactly how transmission is occurring the risk score calculation https://github.com/corona-warn-app/cwa-documentation/blob/master/solution_architecture.md#risk-score-calculation https://github.com/corona-warn-app/cwa-documentation/blob/ma... may be wildly inaccurate too resulting in the wrong people being notified. And even assuming perfect ability to deduce the risk of infection of two people using the app, will that help in the bigger context. If the people most at risk don't install this app and the least at risk do then you may be drawing resources away from the people that most need help.

uvw 6y ago
I imagine it's not meant to be 100% accurate. If it identifies even 50% of the people that may have come in contact with someone who's positive, even considering 50% false positives, I would consider it a rousing success.
- Schlaefer 6y ago
  Even if there are 95% false positive: if you're able to test all those people and catch the 5% that might still be a net profit. It comes down to cost. Societies are spending thousands of billions to mitigate the problem, even a slight reduction of that number is a win.
  - w-m 6y ago
    As far as I understand, you would need to send everybody who might have been in contact with someone who's positive into quarantine, right away. You can also test them, but you need to quarantine them immediately, as the virus is transmitted before symptoms show. If you just send everybody who was in contact with a positively tested person into testing (they give samples, send them in, get tested, get the results back), but they keep going about their normal lives, they will statistically infect more people before the tests come back. So the false positive rate is quite important, as it potentially means sending thousands of people into home-quarantine.
    - Schlaefer 6y ago
      > So the false positive rate is quite important, as it potentially means sending thousands of people into home-quarantine. Of course it's important and of the course the lower the false positive rate the better. But the argument remains: even with a high false positive rate, what's the net result? Maybe overall it's worth putting thousands of false positive in quarantine now than a whole city of millions two months later. There are so many variables and known unknowns in this approach. I argue that even with all the well reasoned arguments against, at this scale and with this stakes they stay theoretical until we actually do it. Let's try at least once, and if it fails it's still knowledge gained.
    - arrrg 6y ago
      False positives do matter. However, we are currently at about 300 new cases per day in Germany. So how much do they matter, really? If everyone of those has the app installed and has, on average, 100 registered contacts (so that’s about 98 false positives, if we assume that on average two of those lead to infections) that’s about 30,000 people being told to isolate every day. If they are told to isolate for one week (should be sufficient, on balance) that’s around 200,000 people isolated at any one point in time. If only 50% have the app installed that’s down to 100,000 people. Sounds high but ok to me. Given how active the infection currently is in Germany I wouldn’t want false positives be higher than that – but somewhere in that high ballpark sounds fine to me.
  - tinus_hn 6y ago
    If 20 times as much people as necessary are forced into a useless 14 day quarantine that is not a net profit.
    - deleted 6y ago
      [deleted]
    - arrrg 6y ago
      The idea is that aggressive quarantining allows a comfortable return to normalcy for everyone. Maybe at most a couple 10,000 sent into home isolation (a week should be plenty here, no need for 14 days – we aren’t shooting for perfect anyways) versus 81 million with strong measures. Obviously the app isn’t the perfect solution here. Much more important is thorough and swift real contact tracing (followed by quarantine irrespective of diagnostics, so quite similar to how the app would work with many false positives). But I wouldn’t reject the app out of hand.
fabian2k 6y ago
The biggest risk are longer contacts, not very short ones. You don't want to notify everyone that passed that person on the street, but you do want to notify everyone that was reasonably close in the same train for half an hour. This is pretty much just an extension to classic contact tracing. And there you also have to work with very rough categories of risk, this isn't so much different.
- Someone 6y ago
  I don’t see why N S-second contacts would be lower risk than one N×S-second one. This isn’t a matter of ‘small doses can’t harm you’, is it?
  - celticninja 6y ago
    Viral load does seem to play a part in severity of the response by the immune system
  - CaptainZapp 6y ago
    Actually it makes a huge difference. You need to absorb a certain amount of payload in oder to get infected. I found this article[1] on the subject extremely enlightening. [1] https://www.erinbromage.com/post/the-risks-know-them-avoid-them https://www.erinbromage.com/post/the-risks-know-them-avoid-t...
    - tzs 6y ago
      One thing unclear from that is how how fast, if at all, accumulated viruses clear out. Say you need to inhale 1000 of a particular virus to get its disease, and talking normally with an infected person gives you 200/minute, so it takes you 5 minutes to get the disease. You can get that 1000 by talking 5 minutes with one infected person, or you can get it by talking 3 minutes with one infected person and then shortly afterwards 2 minutes with another. But what if the gap between those two is longer? I'd guess that the first 600 you got get into cells quickly and start reproducing, but there are few enough that your immune system is able to handle them. The reason you need 1000 is that is the tipping point where the viruses can reproduce faster than your immune system can handle. If that's the case, then after you get that first 600, how many you need to get on the next exposure would be 400 shortly after the first, but as the time between exposures increases that would increase. The model here would be that you have a virus accumulator (you), being filled by exposure events and drained by your immune system, and you get sick if the accumulator reaches some threshold. This makes me wonder if my approach to shopping during this pandemic is wrong. I've been doing a big shopping trip every 3 or 4 weeks, as opposed to before the pandemic when I'd pop in to the store 3 or 4 times a week and only buy a few things. Those big trips involve being in the store for an hour or more (and it's not linear--the time to fill my cart is linear in the number of things I'm buying, but checkout time goes up faster because organizing my stuff at the self-checkout becomes harder). If someone else in the store is infected, I could potentially be around them enough to also get infected. The old small trips only involve a few minutes in the store. If someone else is infected I'm not going to be in there long enough to get an infectious dose from them unless they do something like cough near me. With my mask, and care to avoid other people who are not wearing masks, my realistic risk from an infected person is less than an infectious dose. If my immune system can clear that out in a few days, then I should be good to go for the next short trip. As long as the prevalence of infected people in my community is low enough that I'm not going to get an infectious dose in a single short trip, this should be a safe approach. Another question: suppose I get that 600 dose, and no more, so my immune system handles it fine and I don't get sick. Am I spreading the virus during this time, or do I only start spreading after I get an infectious dose worth of accumulated exposure? Edit: how does acquiring immunity fit in? If I get 60% of an infectious dose and then no further exposure until my body has dealt with that, do I get any immunity or does that only happen if I accumulate enough virus at one time to actually get sick?
rsynnott 6y ago
Many countries are now in the situation where they have far more test capacity than referrals for tests. In that context, this sort of app may be useful; it will produce candidates for tests who are more likely to be hits than purely random testing. This is especially the case in places where prevalence of the disease is now extremely low (like Germany).
zwaps 6y ago
As others have pointed out, resources are currently available. Especially in Germany. Nevertheless, countries who have been successful in reducing the spread also need to find ways to drive R0 below 1 for a long time. This has proven difficult in Germany. Therefore, it seems that any reasonable false positive rate will still be a net benefit - given that active cases are now very low and it is desirable to catch any infections early. So yes, this will not help everyone. And yes, it may lead to false positive quarantines - until test results are back. But it still seems to be a net positive as long as the privacy part is intact.
PeterStuer 6y ago
I have pointed out the weakness of the correlation between viral transmission vectors and BTLE radio signals these apps are relying on a few times before here on HN. I've pointed to the failure of deployment % reaching anywhere near the required density (and we are talking order of magnitude off here, not 'just missing a few %') where citizens had free choice. We've already seen many authorities requesting 'more control' and lambasting Google/Apple for being too restrictive. But on HN, any criticism of this tech is met with a swift unsubstantiated down-vote.
- hn23 6y ago
  It is because tech people think of tech solutions. Just as this whole pandemic was handled in the countries by virologists - who think in terms of viruses. Reading about the app I remembered the book of Hans Rosling ("Factfulness") where he describes a situation in Africa during an Ebola outbreak. He wrote: There where people with apps everywhere. The apps were the hammers looking for nails. However, it just consumed resources and shadowed the fact that numbers reported were just messy and the epidemic was over 14 days ago. In the end they had to do data cleaning and they managed _Ebola_ without an app. I think this app will make people become accustomed to getting traced for $reason.

uvw 6y ago

I imagine it's not meant to be 100% accurate. If it identifies even 50% of the people that may have come in contact with someone who's positive, even considering 50% false positives, I would consider it a rousing success.

Schlaefer 6y ago
Even if there are 95% false positive: if you're able to test all those people and catch the 5% that might still be a net profit. It comes down to cost. Societies are spending thousands of billions to mitigate the problem, even a slight reduction of that number is a win.
- w-m 6y ago
  As far as I understand, you would need to send everybody who might have been in contact with someone who's positive into quarantine, right away. You can also test them, but you need to quarantine them immediately, as the virus is transmitted before symptoms show. If you just send everybody who was in contact with a positively tested person into testing (they give samples, send them in, get tested, get the results back), but they keep going about their normal lives, they will statistically infect more people before the tests come back. So the false positive rate is quite important, as it potentially means sending thousands of people into home-quarantine.
  - Schlaefer 6y ago
    > So the false positive rate is quite important, as it potentially means sending thousands of people into home-quarantine. Of course it's important and of the course the lower the false positive rate the better. But the argument remains: even with a high false positive rate, what's the net result? Maybe overall it's worth putting thousands of false positive in quarantine now than a whole city of millions two months later. There are so many variables and known unknowns in this approach. I argue that even with all the well reasoned arguments against, at this scale and with this stakes they stay theoretical until we actually do it. Let's try at least once, and if it fails it's still knowledge gained.
  - arrrg 6y ago
    False positives do matter. However, we are currently at about 300 new cases per day in Germany. So how much do they matter, really? If everyone of those has the app installed and has, on average, 100 registered contacts (so that’s about 98 false positives, if we assume that on average two of those lead to infections) that’s about 30,000 people being told to isolate every day. If they are told to isolate for one week (should be sufficient, on balance) that’s around 200,000 people isolated at any one point in time. If only 50% have the app installed that’s down to 100,000 people. Sounds high but ok to me. Given how active the infection currently is in Germany I wouldn’t want false positives be higher than that – but somewhere in that high ballpark sounds fine to me.
- tinus_hn 6y ago
  If 20 times as much people as necessary are forced into a useless 14 day quarantine that is not a net profit.
  - deleted 6y ago
    [deleted]
  - arrrg 6y ago
    The idea is that aggressive quarantining allows a comfortable return to normalcy for everyone. Maybe at most a couple 10,000 sent into home isolation (a week should be plenty here, no need for 14 days – we aren’t shooting for perfect anyways) versus 81 million with strong measures. Obviously the app isn’t the perfect solution here. Much more important is thorough and swift real contact tracing (followed by quarantine irrespective of diagnostics, so quite similar to how the app would work with many false positives). But I wouldn’t reject the app out of hand.

fabian2k 6y ago

The biggest risk are longer contacts, not very short ones. You don't want to notify everyone that passed that person on the street, but you do want to notify everyone that was reasonably close in the same train for half an hour. This is pretty much just an extension to classic contact tracing. And there you also have to work with very rough categories of risk, this isn't so much different.

Someone 6y ago
I don’t see why N S-second contacts would be lower risk than one N×S-second one. This isn’t a matter of ‘small doses can’t harm you’, is it?
- celticninja 6y ago
  Viral load does seem to play a part in severity of the response by the immune system
- CaptainZapp 6y ago
  Actually it makes a huge difference. You need to absorb a certain amount of payload in oder to get infected. I found this article[1] on the subject extremely enlightening. [1] https://www.erinbromage.com/post/the-risks-know-them-avoid-them https://www.erinbromage.com/post/the-risks-know-them-avoid-t...
  - tzs 6y ago
    One thing unclear from that is how how fast, if at all, accumulated viruses clear out. Say you need to inhale 1000 of a particular virus to get its disease, and talking normally with an infected person gives you 200/minute, so it takes you 5 minutes to get the disease. You can get that 1000 by talking 5 minutes with one infected person, or you can get it by talking 3 minutes with one infected person and then shortly afterwards 2 minutes with another. But what if the gap between those two is longer? I'd guess that the first 600 you got get into cells quickly and start reproducing, but there are few enough that your immune system is able to handle them. The reason you need 1000 is that is the tipping point where the viruses can reproduce faster than your immune system can handle. If that's the case, then after you get that first 600, how many you need to get on the next exposure would be 400 shortly after the first, but as the time between exposures increases that would increase. The model here would be that you have a virus accumulator (you), being filled by exposure events and drained by your immune system, and you get sick if the accumulator reaches some threshold. This makes me wonder if my approach to shopping during this pandemic is wrong. I've been doing a big shopping trip every 3 or 4 weeks, as opposed to before the pandemic when I'd pop in to the store 3 or 4 times a week and only buy a few things. Those big trips involve being in the store for an hour or more (and it's not linear--the time to fill my cart is linear in the number of things I'm buying, but checkout time goes up faster because organizing my stuff at the self-checkout becomes harder). If someone else in the store is infected, I could potentially be around them enough to also get infected. The old small trips only involve a few minutes in the store. If someone else is infected I'm not going to be in there long enough to get an infectious dose from them unless they do something like cough near me. With my mask, and care to avoid other people who are not wearing masks, my realistic risk from an infected person is less than an infectious dose. If my immune system can clear that out in a few days, then I should be good to go for the next short trip. As long as the prevalence of infected people in my community is low enough that I'm not going to get an infectious dose in a single short trip, this should be a safe approach. Another question: suppose I get that 600 dose, and no more, so my immune system handles it fine and I don't get sick. Am I spreading the virus during this time, or do I only start spreading after I get an infectious dose worth of accumulated exposure? Edit: how does acquiring immunity fit in? If I get 60% of an infectious dose and then no further exposure until my body has dealt with that, do I get any immunity or does that only happen if I accumulate enough virus at one time to actually get sick?

rsynnott 6y ago

Many countries are now in the situation where they have far more test capacity than referrals for tests. In that context, this sort of app may be useful; it will produce candidates for tests who are more likely to be hits than purely random testing. This is especially the case in places where prevalence of the disease is now extremely low (like Germany).

zwaps 6y ago

As others have pointed out, resources are currently available. Especially in Germany. Nevertheless, countries who have been successful in reducing the spread also need to find ways to drive R0 below 1 for a long time. This has proven difficult in Germany. Therefore, it seems that any reasonable false positive rate will still be a net benefit - given that active cases are now very low and it is desirable to catch any infections early. So yes, this will not help everyone. And yes, it may lead to false positive quarantines - until test results are back. But it still seems to be a net positive as long as the privacy part is intact.

PeterStuer 6y ago

I have pointed out the weakness of the correlation between viral transmission vectors and BTLE radio signals these apps are relying on a few times before here on HN. I've pointed to the failure of deployment % reaching anywhere near the required density (and we are talking order of magnitude off here, not 'just missing a few %') where citizens had free choice. We've already seen many authorities requesting 'more control' and lambasting Google/Apple for being too restrictive. But on HN, any criticism of this tech is met with a swift unsubstantiated down-vote.

hn23 6y ago
It is because tech people think of tech solutions. Just as this whole pandemic was handled in the countries by virologists - who think in terms of viruses. Reading about the app I remembered the book of Hans Rosling ("Factfulness") where he describes a situation in Africa during an Ebola outbreak. He wrote: There where people with apps everywhere. The apps were the hammers looking for nails. However, it just consumed resources and shadowed the fact that numbers reported were just messy and the epidemic was over 14 days ago. In the end they had to do data cleaning and they managed _Ebola_ without an app. I think this app will make people become accustomed to getting traced for $reason.