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Tuesday, June 30, 2009

Do Tipping Points Exist?

Are tipping points "mythological"?:

The Tipping Point: Fascinating but Mythological?, by William Easterly: The “tipping point” is a popular concept covering a whole range of phenomena (and a best-selling book by Malcolm Gladwell) where individual behavior depends on the behavior of the herd.

Its original application was to racial segregation. Nobel Laureate Thomas Schelling developed a beautifully simple model for this. Suppose that whites have different degrees of racism – some would “tolerate” higher shares of nonwhites than others. Schelling showed that the less racist whites would still wind up exiting during tipping because of a chain reaction. At first only the most extreme racist whites exit. But their departure causes the white share to go down, making the second most extreme racist whites uncomfortable, so they also exit. The white share goes down some more, and so now even less racist whites will be uncomfortable being a white minority, and they will wind up exiting too. So the remarkable prediction of the tipping point model is that just a little bit of integration that directly bothered only the most racist whites wound up causing ALL of the whites to exit. So even if the typical white was perfectly happy with integrated neighborhoods, these neighborhoods would be so unstable that the final outcome would be extreme racial segregation. ...

It’s easy to imagine development applications for the tipping point idea. Suppose that people decide to get highly educated based on what is the share of highly educated people in the population. After all, it’s only worthwhile being educated if you can talk to and work with a lot of other highly educated people. If the share of educated people falls below a tipping point, a lot of people will stop getting highly educated, which decreases even further the incentive to get highly educated, and we get the same kind of chain reaction... Assuming that low education causes poverty, this is a “poverty trap” story of low education and underdevelopment.

The tipping point stories are fascinating, but do we observe them in the real world? I got intrigued with this question a while ago, and eventually published a paper testing the predictions of the tipping point story (ungated version here) for its original application: racial segregation of US neighborhoods (reminder to self: my job is not only to blog, also to be a full time academic researcher that must “publish or perish”). The basic prediction is that mixed neighborhoods are unstable but segregated neighborhoods are stable. Data on American neighborhoods from 1970 to 2000 rejected these predictions – it was the segregated neighborhoods that were unstable. There was as much “white flight” out of all-white neighborhoods as there was out of mixed neighborhoods, and there was a white influx into segregated nonwhite neighborhoods. Neighborhoods are still very segregated in the year 2000, but not because of tipping. ...

Of course, this is only one test of the tipping point for racial segregation over one time period. Maybe the tipping point is real in other contexts. But think twice and check for evidence before you accept popular stories like the Tipping Point.

    Posted by on Tuesday, June 30, 2009 at 11:27 AM in Economics | Permalink  TrackBack (0)  Comments (17)


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