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  • As a researcher, every once in a while

  • you encounter something

  • a little disconcerting.

  • And this is something that changes your understanding of the world around you,

  • and teaches you that you're very wrong

  • about something that you really believed firmly in.

  • And these are unfortunate moments,

  • because you go to sleep that night

  • dumber than when you woke up.

  • So, that's really the goal of my talk,

  • is to A, communicate that moment to you

  • and B, have you leave this session

  • a little dumber than when you entered.

  • So, I hope I can really accomplish that.

  • So, this incident that I'm going to describe

  • really began with some diarrhea.

  • Now, we've known for a long time the cause of diarrhea.

  • That's why there's a glass of water up there.

  • For us, it's a problem, the people in this room.

  • For babies, it's deadly.

  • They lack nutrients, and diarrhea dehydrates them.

  • And so, as a result, there is a lot of death,

  • a lot of death.

  • In India in 1960,

  • there was a 24 percent child mortality rate,

  • lots of people didn't make it. This is incredibly unfortunate.

  • One of the big reasons this happened was

  • because of diarrhea.

  • Now, there was a big effort to solve this problem,

  • and there was actually a big solution.

  • This solution has been called, by some,

  • "potentially the most important medical

  • advance this century."

  • Now, the solution turned out to be simple.

  • And what it was was oral rehydration salts.

  • Many of you have probably used this.

  • It's brilliant. It's a way to get sodium

  • and glucose together so that when you add it to water

  • the child is able to absorb it even during situations of diarrhea.

  • Remarkable impact on mortality.

  • Massive solution to the problem.

  • Flash forward: 1960, 24 percent child mortality

  • has dropped to 6.5 percent today.

  • Still a big number, but a big drop.

  • It looks like the technological problem is solved.

  • But if you look, even today

  • there are about 400,000 diarrhea-related deaths

  • in India alone.

  • What's going on here?

  • Well the easy answer is, we just haven't gotten those salts

  • to those people.

  • That's actually not true.

  • If you look in areas where these salts are completely available,

  • the price is low or zero, these deaths still continue abated.

  • Maybe there's a biological answer.

  • Maybe these are the deaths that simple rehydration

  • alone doesn't solve. That's not true either.

  • Many of these deaths were completely preventable,

  • and this what I want to think of as the disconcerting thing,

  • what I want to call "the last mile" problem.

  • See, we spent a lot of energy, in many domains --

  • technological, scientific, hard work,

  • creativity, human ingenuity --

  • to crack important social problems with technology solutions.

  • That's been the discoveries of the last 2,000 years,

  • that's mankind moving forward.

  • But in this case we cracked it,

  • but a big part of the problem still remains.

  • Nine hundred and ninety-nine miles went well,

  • the last mile's proving incredibly stubborn.

  • Now, that's for oral rehydration therapy.

  • Maybe this is something unique about diarrhea.

  • Well, it turns out -- and this is where things get really disconcerting --

  • it's not unique to diarrhea.

  • It's not even unique to poor people in India.

  • Here's an example from a variety of contexts.

  • I've put a bunch of examples up here.

  • I'll start with insulin, diabetes

  • medication in the U.S.

  • OK, the American population.

  • On Medicaid -- if you're fairly poor you get Medicaid,

  • or if you have health insurance -- insulin is pretty straightforward.

  • You get it, either in pill form or you get it as an injection;

  • you have to take it every day to maintain your blood sugar levels.

  • Massive technological advance:

  • took an incredibly deadly disease, made it solvable.

  • Adherence rates. How many people are taking their insulin every day?

  • About on average, a typical person is taking it 75 percent of the time.

  • As a result, 25,000 people a year go blind,

  • hundreds of thousands lose limbs, every year,

  • for something that's solvable.

  • Here I have a bunch of other examples,

  • all suffer from the last mile problem.

  • It's not just medicine.

  • Here's another example from technology:

  • agriculture. We think

  • there's a food problem, so we create new seeds.

  • We think there's an income problem, so we create

  • new ways of farming that increase income.

  • Well, look at some old ways, some ways that we'd already cracked.

  • Intercropping. Intercropping really increases income.

  • Sometimes in rice we found incredible increases in yield

  • when you mix different varieties of rice side by side.

  • Some people are doing that,

  • many are not. What's going on?

  • This is the last mile.

  • The last mile is, everywhere, problematic.

  • Alright, what's the problem?

  • The problem is this little three-pound machine

  • that's behind your eyes and between your ears.

  • This machine is really strange,

  • and one of the consequences is that people are weird.

  • They do lots of inconsistent things.

  • (Applause)

  • They do lots of inconsistent things.

  • And the inconsistencies

  • create, fundamentally, this last mile problem.

  • See, when we were dealing with our biology, bacteria,

  • the genes, the things inside here, the blood?

  • That's complex, but it's manageable.

  • When we're dealing with people like this?

  • The mind is more complex.

  • That's not as manageable, and that's what we're struggling with.

  • Let me go back to diarrhea for a second.

  • Here's a question that was asked in the National Sample Survey,

  • which is a survey asked of many Indian women:

  • "Your child has diarrhea.

  • Should you increase, maintain or decrease the number of fluids?"

  • Just so you don't embarrass yourselves, I'll give you the right answer:

  • It's increase.

  • Now, diarrhea's interesting

  • because it's been around for thousands of years,

  • ever since humankind really

  • lived side by side enough to have really polluted water.

  • One Roman strategy that was very interesting

  • was that -- and it really gave them a comparative advantage --

  • they made sure their soldiers didn't drink

  • even remotely muddied waters.

  • Because if some of your troops get diarrhea they're not that effective

  • on the battlefield.

  • So, if you think of Roman comparative advantage part of it was the breast shields,

  • the breastplates, but part of it was drinking the right water.

  • So, here are these women. They've seen their parents

  • have struggled with diarrhea, they've struggled with diarrhea,

  • they've seen lots of deaths. How do they answer this question?

  • In India, 35 to 50 percent say "Reduce."

  • Think about what that means for a second.

  • Thirty-five to 50 percent of women

  • forget oral rehydration therapy,

  • they are increasing --

  • they are actually making their child

  • more likely to die through their actions.

  • How is that possible?

  • Well, one possibility -- I think that's how most people respond to this --

  • is to say, "That's just stupid."

  • I don't think that's stupid.

  • I think there is something very profoundly right in what these women are doing.

  • And that is, you don't put water

  • into a leaky bucket.

  • So, think of the mental model that goes behind reducing the intake.

  • Just doesn't make sense.

  • Now, the model is intuitively right.

  • It just doesn't happen to be right about the world.

  • But it makes a whole lot of sense at some deep level.

  • And that, to me, is the fundamental challenge

  • of the last mile.

  • This first challenge is what I refer to as the persuasion challenge.

  • Convincing people to do something --

  • take oral rehydration therapy, intercrop, whatever it might be --

  • is not an act of information:

  • "Let's give them the data,

  • and when they have data they'll do the right thing."

  • It's more complex than that.

  • And if you want to understand how it's more complex

  • let me start with something kind of interesting.

  • I'm going to give you a little math problem,

  • and I want you to just yell out the answer as fast as possible.

  • A bat and a ball together cost $1.10.

  • The bat costs a dollar more than the ball.

  • How much does the ball cost? Quick.

  • So, somebody out there says, "Five."

  • A lot of you said, "Ten."

  • Let's think about 10 for a second.

  • If the ball costs 10, the bat costs...

  • this is easy, $1.10.

  • Yeah. So, together they would cost $1.20.

  • So, here you all are, ostensibly educated people.

  • Most of you look smart.

  • The combination of that produces

  • something that is actually, you got this thing wrong.

  • How is that possible? Let's go to something else.

  • I know algebra can be complicated.

  • So, let's dial this back. That's what? Fifth grade? Fourth grade?

  • Let's go back to kindergarten. OK?

  • There's a great show on American television that you have to watch.

  • It's called "Are You Smarter Than a Fifth Grader?"

  • I think we've learned the answer to that here.

  • Let's move to kindergarten. Let's see if we can beat five-year-olds.

  • Here's what I'm going to do: I'm going to put objects on the screen.

  • I just want you to name the color of the object.

  • That's all it is. OK?

  • I want you to do it fast, and say it out loud with me,

  • and do it quickly. I'll make the first one easy for you.

  • Ready? Black.

  • Now the next ones I want you to do quickly and say it out loud.

  • Ready? Go.

  • Audience: Red. Green.

  • Yellow. Blue. Red.

  • (Laughter)

  • Sendhil Mullainathan: That's pretty good.

  • Almost out of kindergarten.

  • What is all this telling us?

  • You see, what's going on here, and in the bat and ball problem

  • is that you have some intuitive ways of interacting with the world,

  • some models that you use to understand the world.

  • These models, like the leaky bucket,

  • work well in most situations.

  • I suspect most of you --

  • I hope that's true for the rest of you --

  • actually do pretty well with addition and subtraction in the real world.

  • I found a problem, a specific problem

  • that actually found an error with that.

  • Diarrhea, and many last mile problems, are like that.

  • They are situations where the mental model

  • doesn't match the reality.

  • Same thing here:

  • You had an intuitive response to this that was very quick.

  • You read "blue" and you wanted to say "blue," even though you knew your task was red.

  • Now, I do this stuff because it's fun.

  • But it's more profound than fun.

  • I'll give you a good example of how it actually effects persuasion.

  • BMW is a pretty safe car.

  • And they are trying to figure out, "Safety is good.

  • I want to advertise safety. How am I going to advertise safety?"

  • "I could give people numbers. We do well on crash tests."

  • But the truth of the matter is, you look at that car,

  • it doesn't look like a Volvo,

  • and it doesn't look like a Hummer.

  • So, what I want you to think about for a few minutes

  • is: How would you convey safety of the BMW? Okay?

  • So now, while you're thinking about that let's move to a second task.

  • The second task is fuel efficiency. Okay?

  • Here's another puzzle for all of you.

  • One person walks into a car lot,

  • and they're thinking about buying this Toyota Yaris.

  • They are saying, "This is 35 miles per gallon. I'm going to do

  • the environmentally right thing, I'm going to buy the Prius,

  • 50 miles per gallon."

  • Another person walks into the lot,

  • and they're about to buy a Hummer, nine miles per gallon,

  • fully loaded, luxury.

  • And they say, "You know what? Do I need turbo? Do I need this heavyweight car?"

  • I'm going to do something good for the environment.

  • I'm going to take off some of that weight,

  • and I'm going to buy a Hummer that's 11 miles per gallon."