According to a recent study the social networks of smokers have a big role to play in their ability to quite smoking.

In the 1970s, smokers were at the center of their social networks. But as smoking became less accepted, smokers found themselves being pushed to the fringes of the social network. As more and more of their acquaintances stop smoking, even those who are loosely connected, smokers themselves are more likely to quit. (In the graphic above, smokers are represented by the yellow dots.)

And its not just people copying each other - smokers tend to quit in "clusters," indicating more of a "hive intelligence" than just copycats.

You can hear the full report on NPR.