History has many examples of people who have had a huge positive impact on the world.

Irena Sendler saved 2500 Jewish children from the Holocaust by providing them with false identity documents and smuggling them out of the Warsaw ghetto. Norman Borlaug’s research into disease-resistant wheat precipitated the ‘Green Revolution’. They have been credited with saving hundreds of millions of lives. Stanislav Petrov potentially prevented all-out nuclear war simply by being calm under pressure and being willing to disobey orders.

These people might seem like unrelatable heroes, who were enormously brave, or skilled, or who just happened to be in the right place at the right time. But many people can also have a tremendous positive impact on the world, if they choose wisely.

The most straightforward way many people can have a large impact is with their money. For example, a person earning the typical income in the US, who donates 10% of their earnings each year to the Against Malaria Foundation will probably save dozens of lives over their lifetime.

This is such an astonishing fact that it’s hard to appreciate. But current evidence suggests that this is the world that many people live in. People earning average developed-world incomes can probably save dozens of lives by donating to effective global health charities.

But the world appears to be even stranger, because many people have opportunities that look even better than this. How? First, many people can have a greater impact by working directly on important problems than by donating. Second, other causes might prove even more impactful than global poverty and health, as we’ll discuss below.

But how much better than effective donations might the best interventions be?

In most areas of life, we understand that it’s important to base our decisions on evidence and reason rather than guesswork or gut instinct. When you buy a phone, you will read customer reviews to get the best deal. Certainly, you won’t buy a phone which costs 1000 times more than an identical model.

Yet we are not always so discerning when we work on global problems.

In one section of an essay by Dr Toby Ord, they show the number of years of healthy life (measured using DALYs) you can potentially save by donating $1,000 on a particular intervention to reduce the spread of HIV and AIDS.

The best strategy, educating high risk groups, is estimated to be 1,400 times better than the worst. (It’s possible that these estimates might be inaccurate, or might not capture all of the relevant effects. But it seems likely that there are still big differences between interventions.)

We suspect that the difference in intervention effectiveness is similarly large in other cause areas, though we don’t have as clear data as we do in global health. Why do we think this? Partly because, of projects in many domains for which we have data, most don’t appear to have a significant positive impact. And, more optimistically, because there appear to be some interventions which have an enormous impact. But without knowing which experts to trust, or which techniques to trust in one’s own research, it can be very hard to tell these apart.

Which interventions are highest impact remains an important open question. Comparing different ways of doing good is difficult, both emotionally and practically. But these comparisons are vital to ensure we help others as much as we can.

The media often focuses on negative stories.

But in many ways, the world is getting better. Concerted efforts to improve the world have already had phenomenal success. Let’s consider just a few examples. The number of people living under the World Bank’s poverty line has more than halved since 1990. We lived through the Cold War without a single nuclear weapon being used against another country. Over the last few centuries, we have abolished chattel slavery, dramatically decreased the oppression of women, and, in many countries, done a great deal to secure the rights and acceptance of people who are gay, bi, trans or queer.

Nevertheless, many problems remain. Around 800 million people live on less than $2 per day. Climate change and disruptive new technologies have the potential to negatively impact billions of people in the future. Billions of animals, who may well be conscious and morally valuable, spend short lives in inhumane conditions on factory farms. There are so many problems that we need to think carefully about which ones we should prioritise solving.

The cause that you choose to work on is a big factor in how much good you can do. If you choose a cause where it’s not possible to help very many people, or where there just aren’t any good ways to solve the relevant problems, then you will significantly limit the amount of impact you can have.

If, on the other hand, you choose a cause with great prospects and tested solutions, you may have an enormous impact. For instance, some attempts to reduce the suffering of animals seem to be incredibly effective. Just since 2015, a small group of campaigners – with limited budgets – have helped improve the conditions of hundreds of millions of chickens who were suffering in US factory farms.

Many people are motivated to do good, but already have a cause of choice before beginning research. There are lots of reasons for this, such as personal experience with a problem, or having a friend who’s already raising money for a particular organisation.

But if we choose a cause that simply happens to be salient to us, we may overlook the most important problems of our time. Given that most interventions seem to have low impact, we’re likely to focus on something that is not very impactful if we don’t pick carefully. But it may be even worse than this: issues that are salient to us are probably also salient to others like us, so it’s likely there will be lots of other people working on those issues. This might mean that our additional efforts have even less impact. So going with whichever cause we’re first drawn to seems like a bad strategy.

By remaining open to working on different causes, we’re able to change courses to where we can make the biggest difference, without restricting ourselves too early.

How, then, can we figure out which causes we should focus on? Researchers have found the following framework to be useful: Working on a cause is likely to be high impact to the extent that it is:

• Great in scale (they affect many people’s lives, by a great amount)

• Highly solvable (extra resources will do a great deal to address the problem), and

• Highly neglected (few other people are working on addressing them).

On the basis of this reasoning, there are several cause areas that appear particularly likely to be high-impact.

These choices are not set in stone. They simply represent best guesses about where we can have the most impact, given the evidence currently available. As new evidence comes to light that suggests different causes are more promising, we should consider working on those instead. It’s also worth keeping in mind that even if a person is motivated to choose a good cause rather than the best cause, their impact can still be much larger than it might have been.

We’ll discuss three main areas. We start with the more intuitive area of global poverty, then turn to work to improve animal welfare. Finally, we look into less intuitive, but possibly equally impactful, work to improve the long-term future.