Reporting Chains Swallow Extraordinary Evidence

In January I claimed:

An extraordinary claim is usually itself extraordinary evidence … I would be very unlikely to make such claims in situations where I did not have good reasons to think them true.  The times to be more skeptical of unlikely claims are when there is a larger than usual chance that someone would make such a claim even if it were not true. 

Eliezer responded, and then I outlined a formal model.  I now have a working paper.  In it, I consider the effect of people being organized into a reporting chain, such as up the levels of an organization, or from researcher to referee to editor to reporter to editor and so on.  The new interesting result:

When people are organized into a reporting chain, noise levels grow exponentially with chain length; long chains seem incapable of communicating extraordinary evidence.   

For example, imagine disaster frequency was inverse in deaths, that we faced one big enough to kill us all, and that nature gave someone a signal about the casualties, a signal with a (lognormal) standard deviation of a factor of ten.  But imagine the news of this signal passed through a chain of seven noisy people, each of whom adds 10% to the signal standard deviation.  While nature’s signal itself is clear evidence of an unprecedented disaster, the signal that appears at the chain’s end gives a median estimate of about one death; our warning is lost.

This suggests we reduce the length of our reporting chains, such as in efforts to make organizations more innovative by reducing layers of management:

Perhaps we need only the first few levels of reporting the discretion to adapt a claim to context; reports at further levels could be something like “Fred said that our best estimate of disaster deaths is one million."  Another alternative might be to use prediction markets to shorten reporting chains; the person who saw nature’s signal trades in the market, anyone who wants to correct that market price for context does so via trades, and everyone else is referred to the market price. 

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  • idea

    Really like your website debating about bias. Here is an article dealing with similar subject.
    Hope this will lead to a debate about propaganda vs news.

    http://china.notspecial.org/archives/2007/03/subtle_propagan.html

  • Dagon

    If people in the reporting chain are aware of the noise added by the chain itself (and I think most are), they can refresh the claim by confirming it themselves.

    Unless the a single link in the chain is so noisy that it’s not worth the cost to the next link to confirm it, or a link has a very large underestimation of the noise it adds itself, this should allow the claim to go an infinite distance.

    This seems like a good reason that non-confirmable personal evidence tends not to carry the weight of repeatable observation. It’s much harder to correct for errors in the reporting.

  • http://profile.typekey.com/robinhanson/ Robin Hanson

    Dagon, the newspaper you read today has noise in its signal; for what fraction of the articles you read will you “refresh the claim by confirming it” yourself?

  • http://profile.typekey.com/sentience/ Eliezer Yudkowsky

    I liked the “distorting bias term b s’, which reduces honesty.”

  • http://profile.typekey.com/robinhanson/ Robin Hanson

    Eliezer, I actually didn’t notice that until someone else pointed it out. Apparently my subconscious has a sense of humor.

  • http://cob.jmu.edu/rosserjb Barkley Rosser

    OTOH, if a claim is really extraordinary, it may be disbelieved and get
    discounted as it moves through the chain. In that sense, the chain might
    well “swallow” extraordinary evidence in the sense of making it disappear,
    rather than magnifying it, as suggested here.

  • http://profile.typekey.com/robinhanson/ Robin Hanson

    Barkley, in my model the claim is downgraded and discounted as it moves through the chain – that is exactly the sense in which I meant it is swallowed.

  • http://cob.jmu.edu/rosserjb Barkley Rosser

    Apologies. Focused on the part about people adding 10% at each stage.
    We certainly see that also, where an initial report gets magnified because
    it is dramatic, and then becomes more so with the retelling through the chains.

    Hard to know why or how which effect will dominate, the noisy swallowing, or
    the magnification.

  • http://profile.typekey.com/robinhanson/ Robin Hanson

    Barkley, it would be interesting to see what it would take for a model to predict magnification of a report. My model has everyone being close to rational.

  • Dagon

    Dagon, the newspaper you read today has noise in its signal; for what fraction of the articles you read will you “refresh the claim by confirming it” yourself?

    Fraction of the articles I read? Close to 0. Fraction of the articles that make extraordinary claims and interest me enough to pass on? maybe 60%, scaling inversely to ordinariness. We’re only talking about extraordinary claims in which I participate in the reporting chain, right?

    At the least, I tend to note the references of the story, determine what parallel sources may be available, and make it possible for links upstream of me to eliminate my added noise by seeking out the sources I used.

  • http://cob.jmu.edu/rosserjb Barkley Rosser

    Robin,

    I think that a variety of other factors are going to come into play that are not articulated in your setup definitively. Saying people are “close to rational” does not cover all the ground.

    Thus, it depends on what kind of bureaucratic (or hierarchical or chain) setup they are in. Do they get punished for reporting things that seem to outlandish? Do they get rewarded for saving everybody from something unlikely but very dangerous? These alternatives are just a few of the extra elements that can come in to muddy the picture and either muffle or magnify the signal coming from an initially extraordinary report.

  • Dagon

    Thinking more about this, it may be worth distinguishing a couple of different types of reporting mechanisms for different types of claims.

    I was trying to say above that it’s possible to reduce the effective length of the chain, by cutting out middlemen for claims that are repeatable. I’d like to reformulate my thoughts on the matter.

    The vast majority of information is not passed in a chain, but in a network. Each node gets signals from many other nodes, and can make further connections on demand (and at some expense). This network carries claims (X is true) and metaclaims (some node claims X to be true).

    I can believe network partitioning could cause this to behave similarly to the chain model. This could happen due to secrecy or institutional trust barriers, or for uninteresting claims just friction (it being more expensive to establish new connections than refreshing of the claim or metaclaim is worth to a given node).

    If a claim is about a repeatable experiment or observation, it gets even easier – there can be many nodes independently asserting the claim, and you only need a sufficiently good path to one of them to benefit from the knowledge.

    I think this network WILL be susceptible to some types of noise over some types of claims. Selection biases, for instance, are hard to avoid if you have a cost to evaluating each claim, and so want to keep your number of connections down.

  • http://profile.typekey.com/robinhanson/ Robin Hanson

    Dagon, no doubt it is easier for networks to communicate info that can be cheaply and repeatedly generated at will by many dispersed people. Unfortunately the most interesting extraordinary claims are rarely of this sort.

  • http://jed.jive.com Jed Harris

    This discussion has many resonances with Eliezer’s discussion in the next post of the “decay” of knowledge with transmission from generation to generation. In that case we are more or less forced into a linear chain with no way (in the case of e.g. God speaking of Moses) of going back and rechecking the phenomenon. So the decay is structurally inevitable.

    Science of course promotes short chains by encouraging replication and black boxing. Nobody has to “trust” the PCR works — they get PCR materials and equipment and depend on it every day in their lab. All of molecular biology is a distributed daily replication of PCR. And this pattern holds for essentially all major scientific results, although less dramatically.

    At the risk of getting boring, this is another piece of (what should be) a general theory of judgment aggregation. The community around this blog seems to be stepping smartly in that direction.

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