Network over 32 Years’. They had studied health data from
participants in the long-running Framingham Heart Study, based in
the city of Framingham, Massachusetts. As well as suggesting that
obesity could spread between friends, they proposed that there could
be a knock-on effect further into the network, potentially influencing
friends-of-friends and friends-of-friends-of-friends.
The pair subsequently looked at several other forms of social
contagion in the same network, including smoking, happiness,
divorce, and loneliness.[24] It might seem odd that loneliness could
spread through social contacts, but the researchers pointed to what
might be happening at the edge of a friendship network. ‘On the
periphery, people have fewer friends, which makes them lonely, but it
also drives them to cut the few ties that they have left. But before they
do, they tend to transmit the same feeling of loneliness to their
remaining friends, starting the cycle anew.’
These papers have been hugely influential. In the decade after it
was published, the obesity study alone was cited over 4,000 times,
with many seeing the research as evidence that such traits can
spread. But it’s also come under fire. Soon after the obesity and
smoking studies were published, a paper in the British Medical
Journal suggested that Christakis and Fowler’s analysis might have
flagged up effects that weren’t really there.[25] Then mathematician
Russell Lyons wrote a paper arguing that the researchers had made
‘fundamental errors’ and that ‘their major claims are unfounded’.[26]
So where does that leave us? Do things like obesity actually spread?
How do we even work out if behaviour is contagious?
O of social contagion is yawning,
and it’s also one of the easiest forms of contagion to study. Because
it’s common, easy to spot, and the delay from one person’s yawn to
another is relatively short, researchers can look at transmission in
detail.
By setting up lab experiments, several studies have analysed what
makes yawns spread. The nature of social relationships seems to be
particularly important for transmission: the better we know someone,
the more likely it is that we’ll catch their yawn.[27] The transmission