Facebook's new Timeline, and the apps that connect with it, seem to encourage people to make the data they provide even more detailed.

One of our challenges to understanding people is the event horizon of Facebook. We have a relatively deep engagement with people starting when Facebook was created in 2004, but almost nothing prior. Timeline moves us to a world where we know more about the important events that occurred in people's lives, regardless of when they occurred. For instance, you'll see on my timeline that I studied abroad in Japan during high school in the early 1990s, something that I couldn't express before. This allows us to study phenomena across time—for example, how many students are traveling abroad and whether this rate has changed with different presidential administrations.

Does the way that people behave on Facebook have any relation to real-world social behavior, though?

Every time a new communication medium is created, there is a debate about whether it is destructive of friendship and society in general. Facebook has worked to create a network that closely models real-world relationships. In fact, a recent Pew Internet and American Life study of U.S. Facebook users found that over 93 percent of their Facebook friends were people they had previously met offline. At the same time, as Facebook becomes a more integral part of people's communication, it becomes difficult to disentangle what "real-world social behavior" means independent of Facebook.

Can you give an example of a recent "science" finding from your team?

A recent study we just published in the Proceedings of the National Academy of Sciences tells a new story about the way people adopt products and engage with them. The prevailing theories about this process suggested that what influences a person [to] adopt technologies is the number or percentage of friends who have already adopted the same technology, along with a person's threshold for adopting such technologies. Our study shows that it's less about the number of your friends who are using the technology, but more about their diversity. We found that people are much more likely to join Facebook and become engaged when friends from different parts of their lives have already joined and become engaged.

Do you work on understanding how people relate to ads within Facebook?

Some of the work we're interested in understanding is how your friends influence your decisions to engage with advertising and brands. On the one hand, we choose our friends based on similar interests, and so it is likely that we have similar tastes. At the same time, seeing our friends' interests presented to us along with advertising on Facebook may influence our decision to take action. A big question in this area is whether your similarity to your friends or your friends' actions are responsible for you engaging with the ad, and that's a question we're currently studying.