The unpredictability of “cumulative advantage”

I suppose this article from the NYT will be locked away behind a subscription soon, but Duncan J. Watts describes his team’s experiment and suggests that it’s never possible to predict swings in aggregate behaviour (e.g. how popular something is) beforehand simply because “cumulative advantage” is inherently unpredictable.

The reason is that when people tend to like what other people like, differences in popularity are subject to what is called “cumulative advantage,” or the “rich get richer” effect. This means that if one object happens to be slightly more popular than another at just the right point, it will tend to become more popular still. As a result, even tiny, random fluctuations can blow up, generating potentially enormous long-run differences among even indistinguishable competitors — a phenomenon that is similar in some ways to the famous “butterfly effect” from chaos theory. Thus, if history were to be somehow rerun many times, seemingly identical universes with the same set of competitors and the same overall market tastes would quickly generate different winners: Madonna would have been popular in this world, but in some other version of history, she would be a nobody, and someone we have never heard of would be in her place.


Because the long-run success of a song depends so sensitively on the decisions of a few early-arriving individuals, whose choices are subsequently amplified and eventually locked in by the cumulative-advantage process, and because the particular individuals who play this important role are chosen randomly and may make different decisions from one moment to the next, the resulting unpredictability is inherent to the nature of the market. It cannot be eliminated either by accumulating more information — about people or songs — or by developing fancier prediction algorithms, any more than you can repeatedly roll sixes no matter how carefully you try to throw the die.

Some will claim that there are underlying causes responsible for swings in consumption, but it’s always easy to come up with an explanation for something after it has happened (c.f. Snowden’s “retrospective coherence”)

So the writer asserts that at best, expert analyses are only relevant at that particular point in time, and should be treated with skepticism.

Read full article: NYT – Is Justin Timberlake a Product of Cumulative Advantage?

(From Overcoming Bias)


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