Subtitles section Play video Print subtitles 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."