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Me on COVID-19 Contact Tracing Apps

I was quoted in BuzzFeed:

“My problem with contact tracing apps is that they have absolutely no value,” Bruce Schneier, a privacy expert and fellow at the Berkman Klein Center for Internet & Society at Harvard University, told BuzzFeed News. “I’m not even talking about the privacy concerns, I mean the efficacy. Does anybody think this will do something useful? … This is just something governments want to do for the hell of it. To me, it’s just techies doing techie things because they don’t know what else to do.”

I haven’t blogged about this because I thought it was obvious. But from the tweets and emails I have received, it seems not.

This is a classic identification problem, and efficacy depends on two things: false positives and false negatives.

  • False positives: Any app will have a precise definition of a contact: let’s say it’s less than six feet for more than ten minutes. The false positive rate is the percentage of contacts that don’t result in transmissions. This will be because of several reasons. One, the app’s location and proximity systems — based on GPS and Bluetooth — just aren’t accurate enough to capture every contact. Two, the app won’t be aware of any extenuating circumstances, like walls or partitions. And three, not every contact results in transmission; the disease has some transmission rate that’s less than 100% (and I don’t know what that is).

  • False negatives: This is the rate the app fails to register a contact when an infection occurs. This also will be because of several reasons. One, errors in the app’s location and proximity systems. Two, transmissions that occur from people who don’t have the app (even Singapore didn’t get above a 20% adoption rate for the app). And three, not every transmission is a result of that precisely defined contact — the virus sometimes travels further.

Assume you take the app out grocery shopping with you and it subsequently alerts you of a contact. What should you do? 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.

Similarly, assume you take the app out grocery shopping and it doesn’t alert you of any contact. Are you in the clear? No, you’re not. You actually have no idea if you’ve been infected.

The end result is an app that doesn’t work. People will post their bad experiences on social media, and people will read those posts and realize that the app is not to be trusted. That loss of trust is even worse than having no app at all.

It has nothing to do with privacy concerns. The idea that contact tracing can be done with an app, and not human health professionals, is just plain dumb.

EDITED TO ADD: This Brookings essay makes much the same point.

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Worst-Case Thinking Breeds Fear and Irrationality

Here’s a crazy story from the UK. Basically, someone sees a man and a little girl leaving a shopping center. Instead of thinking “it must be a father and daughter, which happens millions of times a day and is perfectly normal,” he thinks “this is obviously a case of child abduction and I must alert the authorities immediately.” And the police, instead of thinking “why in the world would this be a kidnapping and not a normal parental activity,” thinks “oh my god, we must all panic immediately.” And they do, scrambling helicopters, searching cars leaving the shopping center, and going door-to-door looking for clues. Seven hours later, the police eventually came to realize that she was safe asleep in bed.

Lenore Skenazy writes further:

Can we agree that something is wrong when we leap to the worst possible conclusion upon seeing something that is actually nice? In an email Furedi added that now, “Some fathers told me that they think and look around before they kiss their kids in public. Society is all too ready to interpret the most innocent of gestures as a prelude to abusing a child.”

So our job is to try to push the re-set button.

If you see an adult with a child in plain daylight, it is not irresponsible to assume they are caregiver and child. Remember the stat from David Finkelhor, head of the Crimes Against Children Research Center at the University of New Hampshire. He has heard of NO CASE of a child kidnapped from its parents in public and sold into sex trafficking.

We are wired to see “Taken” when we’re actually witnessing something far less exciting called Everyday Life. Let’s tune in to reality.

This is the problem with the “see something, say something” mentality. As I wrote back in 2007:

If you ask amateurs to act as front-line security personnel, you shouldn’t be surprised when you get amateur security.

And the police need to understand the base-rate fallacy better.

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