Editor's note: This interview with Bill Gates was conducted in 2014.

With an endowment of $40 billion (give or take), the Bill & Melinda Gates Foundation has the financial heft to make dramatic changes in hundreds of millions of people’s lives around the world. But how does the organization decide which causes and institutions to fund? Bill Gates, its co-founder and co-chair, has a well-established knack for sifting through complex data sets to find the right pathways for making progress around the globe in health, education and economic development. Scientific American contributing editor W. Wayt Gibbs sat down with Gates to learn more about how he views the world. A shorter excerpt of the interview appeared in the August 2016 article “Health Check for Humanity.” An edited transcript of the full-length interview follows.

In 1993 the World Bank published a World Development Report that you have said was instrumental in your early thinking about how to direct your charitable giving to be most effective in improving global health.
That was a very important document for me. Melinda and I went to Africa in 1993, and that trip got me thinking about how much nutrition people there have, how people live—sometimes not even being able to afford shoes—why so many children die and the different tiers of social development. We had already been doing some things to improve women’s access to contraception because when women can plan their families, they’re healthier and their kids are healthier. But then I saw that World Development Report. We were giving money to PATH [an international charity based in Seattle], which was working both on infectious diseases and contraception. I was having dinner with their board and someone pointed out that, although it may seem counterintuitive, improving the health of children actually works in the long-term to reduce population growth—when fewer kids die, parents choose to have smaller families.

And then I saw in that World Development Report that 12 million children are dying every year. Wow! It was mind-blowing to me that these preventable diseases—pneumonia, diarrhea, malaria and some other infections that infants get—had such a huge impact. That was the first time it dawned on me that it’s not hundreds of different diseases causing most of the problem—it’s a pretty finite number. And I was surprised by the huge disparity between poor countries, where 20 percent of children were dying before the age of five, and rich countries where that number is more like half a percent.

You were an early backer of Christopher Murray and his push to create an independent organization, the Institute of Health Metrics and Evaluation [IHME], to pull together rigorous statistics on human health worldwide largely independently of the WHO [World Health Organization]. How did you two meet and decide on this course?
I met Chris in 2001 when he was working for the WHO and was doing the first-ever ranking of national health systems. Some countries were pushing back because they didn’t like how he ranked things. This idea that somebody should try to pull together the best understanding of health, particularly for poor countries—Chris is an ambitious guy, so from the beginning he wanted to do it for all countries—was an attractive one. So we gave money to the University of Washington to create IHME.

Chris’s theories are always provocative. The one that has received the most attention recently is his belief that there are a lot of adult malaria deaths both inside and outside of Africa. Ninety percent of the field thinks he’s wrong. Within the next five years, that controversy should be brought to ground.

But just the fact that somebody is trying to publish these numbers and put error bars on them focuses the discussion. We want to get the trend lines on these things, and now that IHME has created a central repository, you no longer have to read hundreds of articles and try to assemble the big picture yourself. People can argue over specific numbers but if the right process is in place, the error bars will either get bigger or some study will be done and the state of knowledge will get better.

Chris did the first version, and a lot of people disagreed with the results. So now IHME has set up a governance committee and a formal process [for conducting outside expert peer review]. Chris is supergood but he likes controversy—and he doesn’t back down. He’s been right about a lot of the opinions he has. But for the job of administering the normative database, he’s not absolutely the perfect person. It just happens that he and the team he has built are so good at the technical stuff that he’s the best choice. We’ve added these other structures to make sure that everybody views this as the definitive source of information.

But in a few cases, mainly malaria, there are still some who think his numbers still aren’t right.

But the WHO and other U.N. agencies collect and publish lots of health statistics on countries around the world. Why is it necessary to have a whole separate effort to do that?
The remit of the WHO isn’t a very precise thing. They face a certain paradox: Are they a friend of the countries and just there to help them or are they a critic of the countries?

I love the WHO, and Margaret Chan has done a lot of great things. But it is a U.N. agency, and that creates certain complexities. When Chris was doing country rankings inside the WHO he thought, “Hey, we’re the normative agency, this is exactly the place this work should be done.” But he found out that both funding and their inability to take controversial positions were limiting. Ranking their customers ended up being tough for them to do.

The first time I met with Chris he described what he was doing inside the WHO: “They are really giving me a hard time,” he said, “but I am persevering.” I met him again some time later and he asked whether we would fund it. Eventually, we stepped up to create IHME.

Now that you have been engaged for well over a decade in efforts to improve global health, what would you identify as lessons you have learned that caused you to change your approach in some substantial way?
We’ve had to learn how to build an organization of about 1,200 people. We’ve hired people from the pharmaceutical industry and people who have worked in the field. We’ve had to learn how to work with donors, how to get more visibility for issues that can seem like they are far away and in poor countries. We’ve been learning how to build product-development partnerships to create drugs and vaccines for malaria and tuberculosis—there are about 15 of these partnerships we’ve set up so far. We’ve learned a lot on the science, the advocacy and the delivery.

We’ve been heavily involved in the Global Fund [to Fight AIDS, Tuberculosis and Malaria] and the Global Alliance for Vaccines and Immunization (Gavi). Both have been incredibly successful, literally saving millions of lives, but they’ve had their ups and downs. Like with IHME, you could ask: “Why did you have to create Gavi and Global Fund—why didn’t UNICEF, UNAIDS and WHO do that?”

What’s the answer to that?
Well, UNAIDS probably didn’t need to be created. If WHO was being run as well then as it is now or when Gro Brundtland was the director general, then they probably wouldn’t have created it. But the AIDS crisis occurred at a time when people weren’t sure that WHO had the capability to respond, so they created UNAIDS. U.N. organizations are not very good at taking a lot of money and spending it on projects. They are technical experts who are good at writing reports about things. The Global Fund took on a different mission: taking rich-world money, pooling it together in a smart way, working with countries where HIV, TB and malaria are prevalent, and getting the money out to them. Staying outside of the U.N. structure had some advantages—but it also meant we were in uncharted territory about how much proof we asked countries to provide that the money wasn’t misspent. We’re still working on finding the right balance.

Let’s talk about the Global Burden of Disease study. [The GBD is published on a nearly annual basis by the IHME.] Because this study is an independent and now—with the additional funding your foundation is providing—a regularly updated assessment of global health, it could in principle serve as a gold-standard reference of progress in various parts of the world on various diseases. Have you actually used it in that way to identify programs that are working and those that are not working and need redirection?
The GBD assembles data from lots of different field studies, many of which we are funding. For example, we ran a big study called GEMS [Global Enteric Multicenter Study] to try to figure out all the different causes of diarrheal disease—rotavirus is the biggest cause, but there’s also E. coli, shigella, cryptosporidium and others—and how important each one is. We still struggle with large uncertainty about the locations and extent of certain diseases, such as typhoid and cholera, which no country wants to admit they still have. My teams, like others who are very active in fieldwork, usually are looking at the primary papers as soon as they come out in the scientific literature. By the time the information gets aggregated and vetted and incorporated into the GBD database, it should no longer be surprising to us.

But GBD is super helpful when we’re talking to developing countries and saying “Look, here’s what is going on with tuberculosis in your country versus others like yours.” It’s a very important tool to educate people—like the World Development Report was for me. You can see the time progressions and zoom in on any country. It’s one of the better data-visualization sites in the entire Web. It’s super nice. And most people aren’t that up to date on these disease trends—particularly for infectious diseases. So I’ve been taking GBD charts with me when I’ve met with people in Cambodia or Indonesia or even at the French aid agency about trends in francophone Africa. They can reveal when we haven’t set the right priorities—so it’s a very important tool for me. Before I go into strategy meetings, I sometimes look at the GBD to remind myself of the numbers.

We now have enough detailed data to break big illness categories like diarrheal disease apart into separate diseases by the root cause. Even so, the error bars tend to be quite large on these estimates because, unlike in the rich world where disease cases are actually counted and tracked, in the poorer parts of the world we have to rely on sampling and extrapolation. If you happen to sample in places where the condition is unusually prevalent, the extrapolated numbers can be wrong.

That raises an interesting point. One of the potential advantages of having this statistical inference machine that IHME uses to produce the GBD estimates is that you could identify where you would get the most bang for the buck if you did a new study that will improve the empirical input to the system. Has the GBD actually been used to prioritize funding of surveillance in this way?
Oh, yeah. Disease surveillance in the poor world is terrible. While it’s great that we now have this published set of numbers, they have pretty big error bars—and probably some of the error bars should be even bigger than they are shown in the IHME reports. But we’re actively looking at ways to improve the situation. New diagnostics are becoming available, for example, that can check for lots of different diseases by analyzing just a few drops of blood. So rather than running one study after another, each of which has to set up a bunch of different centers just to get data on one kind of disease, we might be able to use clinics that are running all the time and constantly monitoring the prevalence of lots of diseases simultaneously.

We need to know where typhoid and cholera are. It drives us crazy that we don’t really know. In a sense, we’ve had a few diseases that are simple. If the question is, “Where is rotavirus?” the answer is: “Everywhere.” Same with pneumococcus. India is forcing us to prove to them like 10 times over—which is absurd—that they have pneumococcus. The vaccine against pneumococcus is being given in Bangladesh but not in India, so we’ll soon start to see a divergence in respiratory disease rates between the two countries. It’s likely to be fairly dramatic. But now we’re trying to analyze the nonpneumococcus part of pneumonia and find out what is causing that. Do antibiotics still work on that part of the problem? As long as we were picking low-hanging fruit like rotaviral diarrhea or pneumococcal pneumonia, we didn’t actually need much surveillance—they are prevalent everywhere. But now that we’re focusing on the remainder, detailed surveillance is critical to us. The other reason to do surveillance is to catch emerging epidemics.

There is also this great mystery about what kids die of during the first 30 days of life. We’ve been proponents of doing better cause-of-death studies, just in general. The amount of data that is still not gathered is pretty amazing.

For the middle-income countries, it’s turning out that a lot more data exists than the academic community previously understood. China, for example, has a lot of data, and they are fortunately now sharing much more of it. For poorer countries, I don’t think we’ll find too many hidden troves.

A very high percentage of the historical data for the poorer regions are extrapolated off of two survey programs: one called MICS [Multiple Indicator Cluster Surveys] funded by UNICEF and another called DHS [Demographic and Health Survey], which is funded by USAID. In Ethiopia DHS showed a very low vaccination rate whereas administrative data showed a very high vaccination rate. When we dug into the details, we learned that the DHS was asking so many questions that people just got fatigued and gave inaccurate answers.

When we went in and did a specific study and gave people advance warning that we would be asking for vaccine cards, we got a very different result. So although DHS has been usually viewed as the gold standard—because countries often lie and say they are doing better than they are, and the DHS numbers catch them in those lies—here was a case where reality was about midway between what the country was saying and what the DHS survey showed. That’s a little disconcerting.

What’s your high-level impression of the collective health of our species? Are we healthier than we were 20 years ago, and are we headed in the right direction?
We are so much healthier now than in the past. It’s one of those mind-blowing good news stories. Because it is good news, and there is no villain, it doesn’t get the attention it deserves. If you look at countries like Vietnam, Cambodia, Sri Lanka, Rwanda, Ghana—basically all communicable diseases are going down. The only infectious disease we work on that is now going up is dengue. Tuberculosis prevalence is stuck, but deaths are dropping.

Getting rotavirus and pneumococcus vaccine out to every child in the world, that’s a really meaningful thing to do. Now we have to work on those first 30 days after birth. Outside of malarial regions about 60 percent of deaths in kids under five happens in that first month. You can see when you look at the GBD results that once a kid hits age five, their chance of dying is actually pretty low everywhere in the world.

Now it’s still higher in poor countries. But if you take out diseases like HIV and TB that occur primarily among adults, between the ages of five and 40, your chance of dying anywhere in the world isn’t that large. It’s mostly accidental or violent deaths. So whenever people see this “average life expectancy” number, they should realize that’s a weird number because it mixes the number of children dying before age five with deaths of adults. So when life expectancies are depressed, usually that’s either because there is a high level of mortality from HIV or TB epidemics among adults in Africa, or a high child mortality rate.

Yes, the burden of noncommunicable diseases is increasing in developing countries. When the GBD results came out, I got asked a lot whether we would change our priorities because it showed that noncommunicable disease account for such a big chunk of disease. My answer is absolutely not.

We do have a diabetes epidemic. We do have an explosion in medical costs because all the rich-world governments have essentially promised health care that they may not be able to afford—care that includes every new thing that comes along. In the U.S. deaths due to heart disease and some cancers have gone down but overall what people have seen isn’t a dramatic decline in death rates in the past 20 years. On a global basis, though, what’s happened in the last 20 years is incredibly dramatic. Partly that’s because disease burden goes down as incomes rise, and the world has done well at that. But beyond that disease prevalence at any given income level has also declined dramatically, particularly at low-income levels. Measles deaths, to take just one example, used to run several million a year and now have fallen to about 300,000 a year. So this is a mind-blowingly good story.

But most people don’t realize that the first 10 percent you spend on medical care—for vaccines and antibiotics—has this unbelievably high return in better health. Later, more incremental advances like chemotherapy are nice, but their health return per dollar spent is much lower. Health care in the U.S. is so expensive both because the system is inefficient and because it’s mostly delivering treatments that have very low marginal utility. Now I’m not saying that’s wrong, but something like half of all DALYs [Disability-Adjusted Life Years] saved are saved by vaccines, antibiotics and good sanitation.

In the U.S. health benefited during 1900 to 1940 from rising incomes and improved sanitation. Then we got vaccines and antibiotics, which led to that magic age from 1940 on. And maybe we’ll have some miracle in the future for cancer and neurological disease—but even if we do, it will be modest in comparison with the big two that came before.

Global health is going to continue to be a good story. We will eradicate malaria sometime in my lifetime. We will get the diarrhea numbers down very dramatically. Work by Larry Summers, along with Dean Jamison of the University of Washington and others, recently has shown that there is a very plausible path to get almost all of the poor parts of the world to the standard of health that the rich countries had in the 1980s—and to do it by 2035 with better delivery of health care and some new interventions. Now the work needed to get child mortality in all of the countries of coastal Africa down to 2 percent—that is a lot of work. Asia is more on track. The other tough cases are Yemen, Afghanistan and Pakistan.