[w-m]

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]

> 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]

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.