Comment by tastroder | Hacker News Reader

Comment by tastroder | Hacker News Reader

> [...] and Bluetooth -- just aren't accurate enough to capture every contact.

Did I miss his paper on the matter? There's dozens of groups working on this and even with a regular free space model the results seem "good enough" in <2m,15min scenarios for an additional data point.

Most of this seems to leave out that digital contact tracing is not a cure all but a tool to help manual efforts. I somewhat hate the simplification people bring here, that every additional identified contact helps, but dismissing it as "plain dumb" seems rather shallow as well. Sure, false negatives will be a thing, the false negative rate of not doing digital contact tracing at all would be higher by definition. Most of what he outlined can occur in manual contact tracing as well and we still do that, simply because it's necessary.

I haven't seen anything so far that would suggest that digital contact tracing in the poster child Singapore had any of the negative impact he brings to the table here and studies like Ferretti et al. [0] seem to make a pretty good case why it would at least not hurt the overall epidemiological goal.

> It's not accurate enough for you to quarantine yourself for two weeks. And without ubiquitous, cheap, fast, and accurate testing, you can't confirm the app's diagnosis. So the alert is useless.

The time frame and assumptions on testing capability is US centric I assume? If you can get a quick test it would not be two weeks, it's likely quick tests will become more prevalent if this sticks around long enough and testing capability will be raised to sufficient levels. Otherwise yes, false positives would quickly diminish usage.

Of course some of his points are valid and need to be addressed by OS vendors, apps and policy makers, and evaluation of efficacy will be just as critical as teaching the public that having an app does not mean things can go back to normal. There's also plenty of opportunity for abuse even with the commonly decentralized architecture that is at the moment widely agreed upon but none of that supports the allegations of this particular article imho.

The comments similarly bring up things like "surface transmission" as if that mattered at all. If you treat a contact tracing app as an additional data point it becomes much more sensible.

[0] https://science.sciencemag.org/content/early/2020/04/09/scie...

What percentage of the population should install and use this before it becomes useful?

The latest survey in my country said less than 50% were willing to adopt it and the number in the article mentions only 20% in Singapore.

That completely depends on your definition of useful, how people react to a "hit" in the application, and a bunch of other factors honestly.

Figure 3 from the paper I linked contains a heatmap [0] that shows the simulated impact on r in different isolation scenarios vs. completely manual contact tracing. That's where those widely cited 60% adoption come from. In my, non-epidemiologist, view what matters more is that a) the gradient in this is better than completely manual contact tracing and b) I have yet to see anything that suggests it did not help in Singapore. While their product lead [1] is a biased source, he correctly points out that working in tandem with health authorities is critical for these efforts. If these apps aren't made only for technologies sake I do not really see how they would hurt. They have 20% there, quite some experience with outbreaks, and didn't replace it yet so I'd figure 20% would be a good enough data point for other countries to evaluate the approach on the scale of a population. And afterwards they would have to be re-evaluated constantly, just like any other measure politicians and epidemiologists currently propose to address the pandemic. We imho don't have enough data yet to even remotely answer "this amount helps", "this is how good they are" but I don't really see how that justifies these "this isn't perfect so it is dumb" reactions in the other direction.

[0] https://science.sciencemag.org/content/sci/early/2020/04/09/...

[1] https://blog.gds-gov.tech/automated-contact-tracing-is-not-a...

Thanks for taking the time to type out this response. I had scanned the paper you posted and failed to make the link between success to isolate and adoption of the app. It's messy and a bunch of factors come into play, I now understand this better.

I don't oppose a tracking app (it could be an api baked into the os but let's call it an app to simplify things). Maybe I'm wrong but that paper only addressed the (bio)tech side of things instead of also considering the sociological implications.

If governments rely on this app to do the work of human tracers, I think the initial adoption rate will be high but then fall dramatically. This is the sociological effect I'm talking about. What happens if the app flags them as possibly infected? Can they call a hotline to give them information or is it just some automated crap they hear? How many times do you think someone would get a false positive before they uninstall it? It works using bluetooth. How much power drain on their batteries are they willing to accept?

I see this app as an aid to human contact tracing not as a replacement. Maybe this is a naive interpretation, but I see it more useful in this situation:

vector: "On date X I met with Zoe, Alec and Ronnie"

tracer: "There's a fourth with the same timestamp here"

vector: "A fourth?? I don't remember a.. Oh... right... uncle dave was also there"

The problem is companies and some governments have abused privacy information and now the consequence is that people are more reluctant to give this useful info. That's why you need to study this also from a sociological point of view.

Yeah that's fair, especially your last point. In a perfect pandemic-fighting world we could just have an app that did that, the decentralized model adopted won't be that specific. It would be more something along the lines of uncle dave getting a notification. I share your concern on initial adoption, especially since I could not find hard data on places that already implemented apps. I would expect an initial rush and then a plateau instead of WhatsApp like growth as some people expect. As for your specific questions I can only offer a few points on two of them given what we know about the current plan here in Germany, that highly depends on the country and I honestly have not looked at how health authorities work in the US very much.

> What happens if the app flags them as possibly infected? Can they call a hotline to give them information or is it just some automated crap they hear?

The new vendors here in Germany were especially chosen with the argument that they are able to operate 24/7 human phone support. With the decentralized approach they'll get a lot of people flagged and at the moment it seems like the app would suggest to them to call up that number (or likely offer that as an alternative to the other established contact points). Those phone contacts could then talk them through the next steps or, should testing become too limited at any point, through an assessment if testing makes sense for them / voluntary self quarantining can be done / ...

> It works using bluetooth. How much power drain on their batteries are they willing to accept?

In centralized models as proposed by PEPP-PT/ROBERT(France) or NHSX(UK) there's a few ways explored to minimize battery usage on Android, the APIs on the iphone require the screen to be turned on for this use case and must subsequently be horrible for battery usage. The decentralized model that was adopted adopted by many countries is supported by Google/Apple as OS vendors with battery usage and interoperability with other Bluetooth usage in mind, I doubt there will be much of an impact (at least not any that would drive significant user numbers away from voluntary use).

If you can get clusters of people to use it, say everyone in a big office building, it's a lot easier to hit that 20-60% number than in the population as a whole.

IMO these apps will be most useful as a tool to assist manual contact tracing teams at first.

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