> "50% of people follow up correctly" for example seems unrealistic due to a few factors

My assumption was that if the R0 is 3-5, that's small compared to the total number of contacts over the infectious period. That means that the false positive rate is going to be rather high. Given a high false positive rate and some inconvenience with following up, needing to go get tested or go into isolation, either of which mean taking time off work at short notice, people will "take a chance" more often than you'd like and delay getting tested until there are symptoms. But certainly it's not a confident estimtate.

Also, Germany is likely cultrally different, but opt-in social distancing / lockdown lasted fully 3 days in the UK before it became clear that it wasn't going to have the necessary effecity. I can imagine the same thing for compliance with contact tracing recommendations.

> The proposed centralized solution would have to rely on malice to easily identify people that did not follow up correctly since there was no means to do that in it

Right, but this is (aiui) different to the systems in countries like South Korea which use location tracking to ensure that you don't break quarantine. It's a point in the possibility space that must be considered to understand tradeoffs.

> AFAIR adoption in Singapore, which is often used as a reason to use this model in the first place, so far has not been anywhere close to the 50% of 80% of phone users. Many people seem to suggest looking at WhatsApps growth rates for realistic adoption time frames.

You'd hope a massive public information campaign could speed up uptake here. I think I've heard that whatsapp is on 75% of devices in Germany (but I haven't verified that number) which if you assume 80% of the population owning a smartphone, leads to 60% of the population opting in. So that doesn't change the results of the toy model too much (if it was 75% of the population rather than 75% of smartphone owners, that would roughly double the fraction of infection chains terminated compared to the 50% assumption).

These numbers still seem pretty low to me, but again I've got precisely zero expertise here.

> Fraser et al have a few general articles and calculated through scenarios on the matter that might be interesting, maybe you get something out of those

Thanks! I'll read those.

> Many discussions w.r.t. the epidemiological impact of these trade-offs at the moment seem anecdotal because they lack proper validation.

That's worrying. I think there's a possibility here that we're in the zone where privacy-preserving contact tracing has too low effacity to be significant in saving lives, but solutions that are mandatory and come with enforcement are effective. If that turns out to be true, there's a clear tradeoff between individual privacy and saving lives / rescuing countries from economic ruin. If I were the sort of person who wanted to significantly change the narrative around privacy to make it look unacceptably selfish, this might be the sort of crisis I'd see as an oppertunity. And given that this is less information than Google and Apple can access as a mattter of course, constructing the narrative that it should be shared with the health service is easy, if people go that way.

I hope there are people thinking about the case where there's popular support for the tracking being mandatory and non-anonymous, so that there can be proper legal — rather than technical — safeguards to ensure the data is only used for its intended purpose and is destroyed promptly when it's no longer useful for that purpose. The optimistic point of view is that this process will give us the ability to shape the fuure of privacy regulation so that we accept that some entities (Google, Facebook, maybe the Government) have more personal data than we're confortable with, but there are stronger controls on how long that data can last and what it can be used for.