According to a new study, people who quit smoking often give up the habit as part of larger group that includes many people they don't even know.  Experts say this so-called "flocking" effect has implications for public health campaigns aimed at getting smokers to kick the habit.  VOA's Jessica Berman reports.

Researchers at Harvard University Medical School in Massachusetts examined the smoking habits and the extent to which an interconnected social network of 12,000 people quit over a 30-year period. 

The participants were part of a large, ongoing U.S. research project known as the Framingham Heart Study.

Lead author Nicholas Christakis says investigators discovered that when one or more people who knew each other quit smoking at the same time, it had a ripple effect that included other people they did not know.

"In a sense what we found is that whole groups of smokers quit at once," he said.  "People quit in droves.  And these groups are composed not just of the people you know directly, but also people more broadly within the network.  So, your friends', spouses', co-workers' decisions to quit are more broadly associated with your decision to quit."

Researchers refer to their finding as "flocking."

Christakis believes the flocking effect has to do with a change in a social norm, such as the widespread recognition over the past 30 years that smoking is harmful to human health. 

Researchers also found that, as more and more groups of Americans quit smoking the remaining 44 million smokers in this country are becoming increasingly marginalized.

Steven Schroeder is a professor of medicine at the University of California in San Francisco.

Schroeder says the study is good news because it shows that more and more people are yielding to peer pressure to quit.  But he says smokers should not be condemned because they have trouble giving up cigarettes.

"To then heap personal scorn on them and to say they are a pariah and that they shouldn't smoke is, I think, piling on; it's adding insult to injury," he said.  "So, what I try to say in the editorial is have compassion for the smoker even if you disapprove of the smoking."

Howard Koh is professor of public health practice at the Harvard School of Public Health. 

Koh says tobacco control efforts have long been directed toward large groups of unrelated people.  But a new strategy may include using flocks to deliver anti-smoking messages. 

"We need to redouble those efforts and understand that when one person quits it helps not only him and her, but also a whole group of people are influenced around them as well," he explained.

The study on smoking behavior and accompanying editorial, by Steven Schroeder, is published in this week's New England Journal of Medicine.