America has become a nation of quitters. And people who know quitters have become quitters themselves.

According to a massive study spanning the last 32 years, people living in the United States have quit smoking in droves and the number of smokers continues to decrease.

Equally good news, say health-care workers, is that people who opt to snuff out their last cigarette forever have inspired countless others in their social networks to do likewise.

These were the findings of researchers at the Harvard Medical School and the University of California - San Diego who reconstructed the social network of 12,067 quitters. They discovered that smoking cessation occurs in network clusters and is hardly the isolated decision it might feel like to the individual quitter.

“We’ve found that, when you analyze large social networks, entire pockets of people who might not know each other all quit smoking at once,” said Nicholas Christakis, a Harvard Medical School Department of Health Care Policy professor who authored the study along with UCSD researcher James Fowler.

“So if there’s a change in the zeitgeist of this social network, like a cultural shift, a whole group of people who are connected but who might not know each other all quit together.”

Over the last few years, Christakis and Fowler have been analyzing data from the Framingham Heart Study, an ongoing cardiovascular study begun in 1948, re-creating the social patterns contained within the study data to see how health correlates with an individual's social network.

The researchers derived information from archived, handwritten administrative tracking sheets dating back to 1971. All family changes for each study participant, such as birth, marriage, death, and divorce, were recorded. Participants also listed contact information for their closest friends, coworkers and neighbors. Coincidentally, many of these friends and coworkers were also study participants.

Focusing on 5,124 individuals, Christakis and Fowler observed a total of 53,228 social, familial, and professional ties.

The research duo reported last year on how obesity spreads through social networks. Using the same data, they decided to analyze smoking-cessation trends within that same population.

The first and most striking finding was the discovery that, from the larger network perspective, people quit smoking as groups and not as individuals.

“When you look at the entire network over this 30-year period, you see that the average size of each particular cluster of smokers remains roughly the same,” said Fowler. “It's just that there are fewer and fewer of these clusters as time goes on.”

They were able to quantify the person-to-person effects of smoking cessation among married couples, siblings, friends, and coworkers. In addition, they also discovered “quitting cascades” that advanced from person-to-person-to-person.

Education also seems to matter. “We are more influenced by the quitting behavior of others if those people are highly educated,” the researchers said. “To add a further twist, we are also more influenced by others if we ourselves are more educated.”

We see by this, that the educated are not only more influential, but they are also more easily influenced.

“If you look back at 1971, smokers and non-smokers alike were at the centers of social networks,” said Fowler. “For people running companies and having parties, smoking was irrelevant. But during the '80s and '90s we saw a dramatic shift of smokers to the periphery of the social network. Contrary to what we might have thought in high school, smoking has become a

supremely bad strategy for getting popular.”

If decisions to quit cascade through social networks, then this study has provided public health campaigns a powerful new methodology with which to influence behaviors.