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- What we're interested in is social contagion.
How can other sorts of things,
how can ideas, norms, behaviors
spread from person to person
and from person to person to person?
Our initial thought was to look at obesity.
Could we find evidence that as one person gained weight,
it made their friends gain weight,
and then their friends' friends, and friends' friends,
and so forth?
So these are some results of that study.
What we show here is that at one degree of separation,
if your friends are obese,
you've got about a 45% higher likelihood
of being obese yourself.
- [Jake] Right.
- [Nicholas] And if your friends' friends are obese,
you've got a 25% higher likelihood of being obese.
And if your friends' friends' friends are obese,
you've got a 10% higher likelihood of being obese.
And it's only when I get to four degrees of separation.
- [Jake] Wow.
- [Nicholas] Your friends' friends' friends' friends',
that there's no longer a relationship
between that person's body size and your body size.
- [Jake] So the truly amazing thing
is that even though
you may never have met your friends' friend,
their behavior is contagious to you
through the friend you have in common.
Follow up studies have demonstrated
that whether you drink alcohol or not
is contagious within your social network
and so is smoking and taste in music and books.
Both happiness and loneliness are contagious too.
And yet, we are not consciously aware of any of that
because we're making most of the decisions
that shape those behaviors on autopilot.
And that is what gives 21st century hackers so much control
over whether a group of people functions well
or functions poorly.
All they have to do is hack into our autopilot system
and seed a behavior.
And without our even being aware of it,
we will spread that behavior throughout our social network,
either for good or for ill.
- [Nicholas] You take a group of people
and you assemble them one way
with one set of rules of interaction,
and those people are kind to each other
or cooperate or innovate or are healthy.
- Right.
- Or you take the same human beings
and connect them a different way,
and they're none of those things.
They're mean to each other,
they don't learn from each other,
they're unhealthy, they're uninnovative,
they're uncooperative.
Same human beings connected different ways
gives the group different properties.
[Jake] Christakis' goal is to design hacks
that will help entire societies function better.
His latest project
is aimed at improving the health of babies
in rural Honduras with this simple hack.
First, strategically select just a few people in a village.
Next, educate them about best practices,
like only giving babies clean water,
and then count on those people
to make that behavior contagious throughout the village.
- [Nicholas] And in this village over here,
you pick six people at random,
the six yellow dots,
to whom you're going to give some sort of an intervention,
a public health intervention,
a clean water intervention,
a vaccination intervention.
And what I'm trying to do is I'm trying to understand
not what happens
to the people to whom you give the intervention,
but what everyone else in the village does.
- [Jake] The goal is to create hacks
that countries can use
to dramatically improve the health of their citizens
at a cost they can afford.
- [Nicholas] For us, the holy grail
is to be able to provide a kind of multiplication factor
for public health interventions.
So that we recognize that if we only have so much money
and we can only reach 100 people,
maybe rather than targeting 100 people in one village,
maybe we could target 20 people
in each of five different villages
and still get all five villages to change their behavior.
And so now we've multiplied by five
the impact of our intervention
by exploiting some of these ideas
about behavior change and social embeddedness.
- [Nicholas] Incidentally, the same paradigm can hold,
not just for villages in the developing world,
but for classrooms who are trying to get kids to not smoke.
We're trying to get kids to be studious.
We're trying to get them to wear their bicycle helmets.
From workplaces,
we're trying to increase worker safety.
To hospitals,
we're trying to get doctors to wash their hands
or order fewer tests.
This is in my eye,
one of the coolest things you can do in science today.
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