Facebook, Yahoo Test Six Degrees Theory

Duncan Watts on modernizing a 1960s-era experiment

A classic sociology experiment is getting the Facebook treatment. This week, Yahoo Research launched an online study to test the oft-repeated—but as yet unresolved—theory that anyone in the world can reach anyone else in “six degrees of separation.” Using Facebook and its social graph of 750 million users, Yahoo’s “Small World Experiment” invites people worldwide to attempt to send a message to a specified “target” by creating an online chain of connections.

Led by Duncan Watts, principal research scientist at Yahoo Research, the study puts a high-tech spin on a 1967 experiment by Harvard researcher Stanley Milgram. Though its findings were not definitive, it ultimately led to the popular “six degrees” hypothesis.

Cameron Marlow, Facebook’s research scientist and "in-house sociologist," said that because Facebook’s social graph is essentially the best representation of real world relationships available, “our data can speak more definitively to this question than anything else in history.

“We believe that the average distance between two people is shrinking mostly because the types of connections you maintain online are a much better representation of people you know than the set of people you think about on a regular basis,” he said. “The fact that you transcribed all of your relationships into something like Facebook allows you to stay in touch with a much wider audience. This gives us not only a measurement on just how the world actually is but also how well people can utilize those relationships to route messages across the world.”

Adweek chatted with Watts about his study and its noteworthy roots; excerpts follow.


Adweek: Describe the background of the Small World Study.

Watts: In Milgram’s day, he used physical packets and he had just one target, this stock broker who lived just outside of Boston, and he had about 300 people trying to reach the target. The famous result was about 20 percent of the chains got to the target, and the average length of those chains was six degrees.

What was the conclusion?

There are two ways to read this result. One is that the world is small because the chains that got through were shorter—much shorter than people expected. The other way is that most chains didn’t get through, so you might suspect that the reason they didn’t get through is because most chains are actually long and the world is really not connected. A minority of people can reach each other in a small number of steps, but the majority of people cannot.

What’s your hypothesis in this study?

This dual interpretation has replicated itself for all other [similar] experiments. When we re-did this experiment 10 years ago, we used email through a Web interface and we did it on a much, much larger scale. We had 18 different targets around the world and 20,000 people trying to reach them, and we basically got the same sort of result. A small fraction of chains actually reached the targets, and the ones that got through were very short. But, of course, you have to wonder about the ones that did not get through.

The history of this is we have reasonable confidence that [for] the chains that didn’t get through, if people had kept passing them along, then about half of them would get to their targets in seven steps or less. That’s the hypothesis that we’re working with.

How does Facebook help?

The problem that all of the experiments have had—and the problem that we’re trying to address with this one—is that you never really know what the ground truth is. You know that there’s some network out there involved that connects people, and you know that messages are being passed along on top of this network. The problem is because you can’t see the network underneath them, you don’t know whether people are making the right choices, you don’t know if the chains are as short as possible, and you don’t know why the chains that aren’t completing are stopping.

The major difference here is that Facebook [is] the network over which these messages are being passed. We can see through Facebook how everyone is really connected to everyone else. We can see whether people can actually find these short paths. In previous experiments you were missing this background picture, but now we have the background and we can run the experiment on top of it.

So is this experiment testing whether people are actually six degrees apart from one another?

There’s actually two versions of the small world hypothesis. One is what we call topological, [which refers to] the structure of the underlying network. There’s a huge amount of evidence that in different kinds of networks—social networks, neural networks, other kinds of networks—they tend to

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