It’s easy to feel like one can person can’t make a difference. The world has so many big problems, and they often seem impossible to solve.

How much impact do doctors have?

Many people who want to help others become doctors. One of our early readers, Dr. Greg Lewis, did exactly that. “I want to study medicine because of a desire I have to help others,” he wrote on his university application, “and so the chance of spending a career doing something worthwhile I can’t resist.”

So, we wondered: how much difference does becoming a doctor really make? In 2012, we teamed up with Greg to find out, and this work is now being reviewed for publication.

Since a doctor’s main purpose is to improve health, we tried to figure out how much extra “health” one doctor actually adds to humanity. We found that, on average in the course of their career, a doctor in the UK will enable their patients to live an extra combined 140 years of healthy life, either by extending their lifespans or by improving their overall health. There is, of course, a huge amount of uncertainty in this figure, but the real figure is unlikely to be more than ten times higher than 140.1

Using a standard conversion rate (used by the World Bank among other institutions) of 30 extra years of healthy life to one “life saved,” 140 years of healthy life is equivalent to 5 lives saved. This is clearly a significant impact, however it’s less of an impact than many people expect doctors to have.

There are three main reasons for this.

1. Researchers largely agree that medicine has only increased average life expectancy by a few years. Most gains in life expectancy over the last 100 years have instead occurred due to better nutrition, improved sanitation, increased wealth, and other factors.
2. Doctors are only one part of the medical system, which also relies on nurses and hospital staff, as well as overhead and equipment. The impact of medical interventions is shared between all of these elements.
3. Most importantly, there are already a lot of doctors in the developed world, so if you don’t become a doctor, someone else will be available to perform the most critical procedures. Additional doctors therefore only enable us to carry out procedures that deliver less significant and less certain results.

This last point is illustrated by the chart below, which compares the impact of doctors in different countries. The y-axis shows the amount of ill health in the population, measured in Disability-Adjusted Life Years (aka “DALYs”) per 100,000 people, where one DALY equals one year of life lost due to ill health. The x-axis shows the number of doctors per 100,000 people.

DALYs per 100,000 people versus doctors per 100,000 people. We used WHO data from 2004. Line is the best fitting hyperbola determined by non-linear least square regression. Full explanation in this paper.

You can see that the curve goes nearly flat once you have more than 150 doctors per 100,000 people. After this point (which almost all developed countries meet), additional doctors only achieve a small impact on average.

So if you become a doctor in a rich country like the US or UK, you may well do more good than you would in many other jobs, and if you would be an exceptional doctor, then you’ll have a bigger impact than these averages. But it probably won’t be a huge impact.

In fact, in the next article, we’ll show how almost any college graduate can do more to save lives than a typical doctor. And in the guide, we’ll cover many other examples of common but ineffective attempts to do good.

These findings motivated Greg to switch from clinical medicine into public health, for reasons we’ll explain over the rest of the guide.

Who were the highest-impact people in history?

Despite this uninspiring statistic about how many lives a doctor saves, some doctors have had much more impact than this. Let’s look at some examples of the highest-impact careers in history, and see what we might learn from them. First, let’s turn to medical research.

In 1968, while working in a refugee camp on the border of Bangladesh and Burma, Dr. David Nalin discovered a breakthrough treatment for patients suffering from diarrhea. He realised that giving patients water mixed with the right concentration of salt and sugar would rehydrate them at the same rate at which they lost water. This prevented death from dehydration much more cheaply than did the conventional treatment of using an intravenous drip.

Dr. Nalin helped to save millions of lives with a simple innovation: giving diarrhoea patients water mixed with salt and sugar.

Since then, this astonishingly simple treatment has been used all over the world, and the annual rate of child deaths from diarrhea has plummeted from 5 million to 1.3 million. Researchers estimate that the therapy has saved about 50 million lives, mostly children’s.2

If Dr. Nalin had not been around, someone else would, no doubt, have discovered this treatment eventually. However, even if we imagine that he sped up the roll-out of the treatment by only five months, his work alone would have saved about 500,000 lives. This is a very approximate estimate, but it makes his impact more than 100,000 times greater than that of an ordinary doctor:

But even just within medical research, Dr. Nalin is far from the most extreme example of a high-impact career. For example, one estimate puts Karl Landsteiner’s discovery of blood groups as saving tens of millions of lives.3

Leaving the medical field, later in the guide, we’ll cover the story of a hugely impactful mathematician, Alan Turing, and bureaucrat, Viktor Zhdanov.

Or, let’s think even more broadly. Roger Bacon and Galileo pioneered the scientific method, without which none of the discoveries we covered above would have been possible, along with other major technological breakthroughs like the Industrial Revolution. These individuals were able to do vastly more good than even outstanding medical practitioners.

The unknown Soviet Lieutenant Colonel who saved your life

Or consider the story of Stanislav Petrov, a Lieutenant Colonel in the Soviet army during the Cold War. In 1983, Petrov was on duty in a Soviet missile base when early warning systems apparently detected an incoming missile strike from the United States. Protocol dictated that the Soviets order a return strike.

But Petrov didn’t push the button. He reasoned that the number of missiles was too small to warrant a counterattack, thereby disobeying protocol.

If he had ordered a strike, there’s at least a reasonable chance hundreds of millions would have died. The two countries may have even ended up engaged in an all-out nuclear war, leading to billions of deaths and, potentially, the end of civilisation. If we’re being conservative, we might quantify his impact by saying he saved one billion lives. But that could be an underestimate, because a nuclear war would also have devastated scientific, artistic, economic and all other forms of progress leading to a huge loss of life and well-being over the long run. Yet even with the lower estimate, Petrov’s impact likely dwarfs that of Nalin and Landsteiner.

What does this spread in impact mean for your career?

We’ve seen that some careers have had huge positive effects, and some have vastly more than others.

Some component of this is due to luck – the people mentioned above were in the right place at the right time, affording them the opportunity to have an impact that they might not have otherwise received. You can’t guarantee you’ll make an important medical discovery.

But it wasn’t all luck: Landsteiner and Nalin chose to use their medical knowledge to solve some of the most harmful health problems of their day, and it was foreseeable that someone high up in the Soviet military could have a large impact by preventing conflict during the Cold War. So, what does this mean for you?

People often wonder how they can “make a difference”, but if some careers can result in thousands of times more impact than others, this isn’t the right question. Two career options can both “make a difference”, but one could be dramatically better than the other.

Instead, the key question is, “how can I make the most difference?” In other words: what can you do to give yourself a chance of having one of the highest-impact careers? Because the highest-impact careers achieve so much, a small increase in your chances means a great deal.

The examples above also show that the highest-impact paths might not be the most obvious ones. Being an officer in the Soviet military doesn’t sound like the best career for a would-be altruist, but Petrov probably did more good than our most celebrated leaders, not to mention our most talented doctors. Having a big impact might require doing something a little unconventional.

So how much impact can you have if you try, while still doing something personally rewarding? It’s not easy to have a big impact, but there’s a lot you can do to increase your chances. That’s what we’ll cover in the next couple of articles.

But first, let’s clarify what we mean by “making a difference”. We’ve been talking about lives saved so far, but that’s not the only way to do good in the world.

What does it mean to “make a difference?”

Everyone talks about “making a difference” or “changing the world” or “doing good” or “impact”, but few ever define what they mean.

So here’s our definition. Your social impact is given by:

The number of people whose lives you improve, and how much you improve them, over the long-term.

This means you can increase your social impact in three ways: by helping more people, or by helping the same number of people to a greater extent (pictured below), or by doing something which has benefits that last for a longer time.

We think the latter is especially important, because many of our actions affect future generations.

For example, if you improve the quality of government decision-making, you might not see many quantifiable short-term results, but you will have solved lots of other problems over the long term.

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