christakis

"It is possible to put on the TV and really engage with a child verbally, " says Christakis.

Dr Christakis arranged for a collaboration-testing game to be played over the web, with many participants.

Dr. Christakis described watching the vanishing clusters as like lying on your back in a field, looking up at stars that were burning out.

To put it to the test, Dr Christakis and his team made use of two unusual sets of demographic data.

Christakis agreed. When overweight or obesity becomes normal in a given social circle, people may be more likely to become obese themselves.

Dr Christakis and Dr Fowler selected a random group of 319 undergraduates and asked each to nominate up to three friends.

In earlier work, Christakis also documented that baby DVDs and videos may even contribute to a drop in language acquisition in infants.

Dr Christakis used what is known as a public-goods game for his experiment.

"These results may explain the association between infant television exposure and delayed language development, " Christakis said.

But the findings, Dr. Christakis says, could have "profound implications for children's cognitive and social development. "

"Because people are interconnected, their health is interconnected, " said lead author Dr. Nicholas Christakis, a Harvard sociologist.

"We found there appears to be a genetic tendency to introduce your friends to each other, " Christakis said.

"You change your idea of what is an acceptable body type by looking at the people around you, " Dr. Christakis said.

Whether Dick and Harry know each other depends on Tom's genes, " Christakis said in a telephone interview. "

Still, Dr. Christakis said, smoking initiation followed the same patterns as cessation: people started and stopped smoking in groups.

Identifying the most influential or popular people within these networks has become easy, Christakis says, due to advances in data analysis.

The heavy technology use, Dr. Christakis said, "makes reality by comparison uninteresting. "

One approach, says Christakis, is to manipulate the network of connections people have.

Incidentally, the contagion effect also works withweight loss, quitting smoking and happiness, Christakis and Fowler found.

But Christakis says it's hard to distinguish between education and entertainment.

"Each additional happy person makes you happier, " Christakis said.

in Christakis and Fowler's paper, the happiness link remained unbroken.

To find out, Dr Christakis has forged links with some anthropologists.

In the Wisconsin sample, Dr Christakis looked at those who had died before their 65th birthday.

Nicholas Christakis and James Fowler based the study on the emotional health of almost 5000 people.

Dr. Christakis and Dr. Fowler published a similar study last year on obesity, asking about the rise of a health problem.