Social Contagion theory

[Nat Wilcox]

but there is (what seems to be) a related collection of theories of imitative behavior, "herding" and so forth in decision and game theory, plus an experimental literature that looks at it.

You can think of imitation as something a reasonable person 3 might do when only weakly informed themselves, even when their own weak information considered alone recommends non-imitation. Suppose person 3 has weak information favoring action Y over action X. But person 3 also observes that persons 1 and 2 have chosen to take action X rather than Y. Suppose also that person 3 believes that her own information is no better than that of persons 1 and 2, and also believes that her own values and/or goals are not very different from those of persons 1 and 2. Then it may be reasonable for her to completely ignore her own information, and imitate persons 1 and 2.

Now, let person 4 show up, also in the same situation as person 3 was. He sees three people taking action X over Y. And so he too ignores his own information. And so forth. Decisions "herd together" and it becomes reasonable for all subsequent weakly informed decision makers to ignore their own information. Fittingly, the theorists call this an "information cascade."

Interestingly, "reverse cascades" can form when everyone receives only noisy and weak information...these are cascades where everyone takes the "wrong" decision..."wrong" in the sense that, if there was some alternative way to pool everyone's (individually ignored) information publicly, it would be clear that everyone had been fooled into herding on the wrong decision.

As I mentioned, there is some experimental literature on information cascades if anyone is interested in them. I suspect that, for the purposes of this group, information cascades and other kinds of "reasonable herding" are most useful as an idea to keep in mind--simply, that there may be "good reasons" for any actor in a social network to imitate or herd, so that it may be a difficult thing to fight or alter.

It also suggests that one way to break cascades and herds is to supply alternatives to inferring information from the observation of decisions...alternatives that allow for all individuals' weak bits of information to be combined publicly. The whole problem with cascades is that once enough decisions line up so that people ignore their own information in making their own decision, future decisions become uninformative.