[dchyrdvh]

Yes, they all have no value.

Let's assume someone got bankrupted by a hospital over a severe coronavirus case. This means that someone has been wandering around for weeks infecting others. Let's assume there is a chain of 10 contacts between me and that someone. The probability of virus transmission is 1% (and I'm generous here) because more people wear masks, because people avoid talking and generally avoid interactions. Probability of transmission over 10 links is 10^-20 and we may stop right here, unless we plan to study quantum particles.

Now let's assume I get a notification that I might have been infected over the past few weeks. The probability that the app is correct is abysmally low. But even if I get infected, I'm unlikely to get sick and I'm unlikely to transmit the virus to others because masks, social distancing and because I already assume I'm infected.

So yeah, this app would be useless and is only good for surveillance.

[sanderjd]

I don't think you answered the question you're responding to. You're still talking about the app, the question is about all contact tracing generally. Actual epidemiologists appear to disagree with your (I'm assuming) amateur opinion that contact tracing, in general, is useless. They are aware of all the things you mention, and still believe it is useful. There also seems to be examples of success with contact tracing in conjunction with good testing regimes in countries that are faring much better than the US. It seems like arrogance to me to think that we can't learn anything from those successes.

(But I'm very uneasy about these app-based approaches, and much more in favor of hiring tons of humans to do contact tracing instead, or at least as the primary mechanism.)

[SketchySeaBeast]

> The probability of virus transmission is 1% (and I'm generous here) because more people wear masks, because people avoid talking and generally avoid interactions. Probability of transmission over 10 links is 10^-20 and we may stop right here, unless we plan to study quantum particles.

If that were truly the case why are there still transmissions? Wouldn't that imply that in a matter of 5 months it will be impossible to get the disease strictly due to the timeline and required links? ~14 days of transmissible * 10 transmission events / 30 days in a month = 140 days before no more mathematically possible transmissions. Wouldn't that require us being repeatedly exposed to every person on the planet to keep those numbers to a possible level?

[dchyrdvh]

Because there are multiple paths and the virus really spreads like a wave frontier in a 10 dimensional space of human to human contacts graph. The virus also spreads in a non uniform way: it's not about the distance between two interacted persons, but about the nature of their interaction, whether they weared masks and so on. The virus also really likes to stick to surfaces, like door handles or plastic wraps, and this vector of transmission is very difficult to trace even manually. Think of credit cards. The virus floats in the air like smoke if someone coughed and others may catch it this way. An app can't account for that and instead builds a social graph of interactions. The app would notice a lot of people crowded in a parking lot and would assume the virus was transmitted between those 50 people, but it wouldn't know that all those people sit in their cars, so the app just made the transmission chain 50x less useless. A few more such gatherings and the relevance of tracing drops to those sub quantum levels of homeopathic medicine.

[chasd00]

the value is here

"you've come in contact with someone infected! use this coupon code to get 10% off your test at select locations. Need a mask? click here to buy one and save your family".