Otherside of the story, Facebook scholars.

Each day about 1,700 juniors at an East Coast college log on to Facebook.com to accumulate “friends,” compare movie preferences, share videos and exchange cybercocktails and kisses. Unwittingly, these students have become the subjects of academic research.

To study how personal tastes, habits and values affect the formation of social relationships (and how social relationships affect tastes, habits and values), a team of researchers from Harvard and the University of California, Los Angeles, are monitoring the Facebook profiles of an entire class of students at one college, which they declined to name because it could compromise the integrity of their research.

In other words, Facebook — where users rate one another as “hot or not,” play games like “Pirates vs. Ninjas” and throw virtual sheep at one another — is helping scholars explore fundamental social science questions.

Facebook’s network of 58 million active users and its status as the sixth-most-trafficked Web site in the United States have made it an irresistible subject for many types of academic research.

But it is Facebook’s role as a petri dish for the social sciences — sociology, psychology and political science — that particularly excites some scholars, because the site lets them examine how people, especially young people, are connected to one another, something few data sets offer, the scholars say.

“For studying young adults,” said Vincent Roscigno, an editor of The American Sociological Review, “Facebook is the key site of the moment.”

But some scholars point out that Facebook is not representative of the ethnicity, educational background or income of the population at large, and its membership is self-selecting, so there are limits to research using the site. Eszter Hargittai, a professor at Northwestern, found in a study that Hispanic students were significantly less likely to use Facebook, and much more likely to use MySpace. White, Asian and Asian-American students, the study found, were much more likely to use Facebook and significantly less likely to use MySpace.

Facebook began in 2004 at Harvard and was restricted to students until 2006. As Ms. Hargittai points out in her paper, “Requiring such an affiliation clearly limited the number and types of people who could sign up for the service in the beginning.”

But Derrick B. Clifton, 19, a student at Pomona College in California, said, “I don’t feel like academic research has a place on a Web site like Facebook.” He added that if it was going to happen, professors should ask students’ permission.

Professor Hargittai of Northwestern conducted her Facebook study through a writing course that is required of all students at the University of Illinois, Chicago. Some 1,060 participants answered survey questions on paper. Professor Ellison of Michigan State used a random sample of 800 undergraduates who were invited to participate via an e-mail message that included a link to an online survey.

“Employers are looking at people’s online postings and Googling information about them, and I think researchers are right behind them,” said Dr. Christakis, a sociologist and internist who was an author of a study that received wide attention this year for its suggestion that obesity is “socially contagious.” (The researchers did not use Facebook.)

Among other topics, the Harvard-U.C.L.A. researchers are investigating a concept, first put forth by the pioneering German sociologist Georg Simmel, known as triadic closure: whether one’s friends are also friends of one another. If this seems trivial, consider that a study in 2004 in The American Journal of Public Health suggested that adolescent girls who are socially isolated and whose friends are not friends with one another experienced more suicidal thoughts.