Decision to quit smoking taken in groups, study finds

In collaboration with the Press Association

The decision to quit smoking is often taken by entire clusters of spouses, friends, siblings and colleagues rather than isolated individuals, scientists have found.

Experts at Harvard Medical School and the University of California, San Diego, analysed smoking behaviour in a social network of 12,067 people between the ages of 21 and 70 who were connected as family, friends and co-workers over a period of three decades.

Smoking rates were found to follow the national downward trend between 1971 and 2003, but the researchers also noted some interesting trends within the group.

For example, smokers tended to mix equally with non-smokers in 1971, but by 2000 there had been a noticeable change, with smokers and non-smokers tending to form separate clusters and smokers gradually being marginalised on the fringes of the social network.

The researchers also found that people who knew someone who had given up smoking were more likely to give up themselves, and the closer the relationship between the two people, the greater the chance of them both quitting.

When a husband or wife quit, it reduced the likelihood of their spouse smoking by 67 per cent, and when a sibling gave up, this reduced a second sibling's likelihood of smoking by 25 per cent.

A similar trend was found among friends - with the chance of a person smoking decreasing by 36 per cent if their friend had given up - and among employees working in small firms.

"This study has an essential public health message - that no one is an island - our health is partially determined by our social networks and those around us," said Dr Richard Suzman, director of the National Institute on Aging's (NIA's) Division of Behavioural and Social Research.

"The decision to quit smoking cascaded throughout the web, indicating that some form of collective decision-making was taking place. The results suggest new and probably more powerful approaches to changing health behaviours, such as smoking, by careful targeting of small peer groups as well as single individuals," he suggested.

Professor Nicholas Christakis of Harvard Medical School commented: "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. 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.

"Interestingly, geography did not appear to play a role because smoking behaviours spread between contacts living miles apart and in separate households," he noted. "Rather, the closeness of the relationship in the network was key to the spread of smoking behaviours."

The researchers also found that the better-educated the contacts, the greater the influence on smoking behaviour, and that there was no such influence between pairs of friends with a high school education or less.

The report appears in the New England Journal of Medicine.