WASHINGTON: When you stub out that last cigarette, vowing never to light another, you need not feel alone. Chances are your spouse, your best friend and even your co-workers will follow suit.

Even people in your milieu who you don’t know very well are likely to be influenced by your decision to go cold turkey.

That’s the finding of US researchers who analysed relationships among 12,000 people over three decades and found that a steady decrease in smoking over that period occurred in clusters, all along the six degrees of separation.

“We’ve found that when you analyse large social networks, entire pockets of people who might not know each other all quit smoking at once,” said Nicholas Christakis, a professor at Harvard Medical School and co-author of the study.

“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,” he explained.

Investigators reconstructed the social networks of 12,067 individuals during a period from 1971 to 2003, inventorying major life changes such as marriage, death and divorce.

Study participants also listed contact information for close friends, work colleagues and neighbours.

Coincidentally, many of those friends and colleagues had also joined the study, enabling researchers to observe what they said was a total of 53,228 family, social or professional relationships.

The most striking finding of the investigators was that people kicked the habit in clusters, the study authors report in the May 22 edition of the New England Journal of Medicine.

“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 co-author James Fowler of the University of California.

“It’s just that there are fewer and fewer of these clusters as time goes on.”—AFP