If you are reading this review, chances are you in the richest 10% of the world. Luckily, like me, you probably live in a rich country and make more than $16,000 a year. With our money and time we can make a significant difference to the world.

In Doing Good Better, Will MacAskill, co-founder of Giving What We Can, argues that we “should expect to be able to do at least one hundred times as much to benefit other people as you can to benefit yourself” (p. 23). This is because recent studies documenting the relationship between subjective well-being and income suggest that the doubling of income will always increase subjective well-being by the same amount. Hence an extra $28,000 for the typical American wage earner already making $28,000 will increase her subjective well-being as much as an extra $220 would for a poor Indian farmer. MacAskill calls this remarkable idea the 100x Multiplier. We can do 100x more good for others than for ourselves.

But how? There are, after all, so very many different ways we could spend our time and money. Should one make as much money as one can and donate a significant portion of it? Where should one donate to? Or should one work for an NGO? Which one?

Doing Good Better introduces a framework to think about and answer these sorts of questions. In particular, it explains and defends the idea of effective altruism. Effective Altruism starts with asking “How can I make the biggest difference possible?” and then applies careful reasoning and evidence to find an answer.

According to MacAskill, there are five key questions that characterize the thinking of an effective altruist. Suppose we are thinking of choosing a particular cause, charity, or career with the goal of making a significant difference. First, an effective altruist may ask how many people benefit from me doing this, and by how much? Second, even if an activity is beneficial it may be that other activities are better, hence we should ask whether this is the most effective thing we can do. This question is made pressing by the observation that some charities, careers, or causes are much better and more effective than others. For example, MacAskill compares health programs like treating Kaposi’s sarcoma (a cancer that afflicts many with HIV and which tends to cause purple tumors on the skin and mouth) to groups that provide bed nets to combat malaria. He finds that supporting a group like the Against Malaria Foundation is 500 hundred times more effective then treating Kaposi’s sarcoma. This is largely due to the ease, low-cost, and success of providing bed nets.

Third, we should wonder whether this area is neglected. If an area is neglected, one’s efforts will have a much greater impact since the most effective activities, the low-hanging fruit as it were, have not been realized yet. On the other hand, for non-neglected causes the low-hanging fruit has typically already been picked and so by spending one’s time or money on these non-neglected causes one will be making less of a difference than one could have by doing something else. Fourth, an effective altruist will be concerned about what would have happened otherwise. For example, if you are considering doing good as an aid worker, you do not just want to look at the lives that would directly improve, but what would happen if you do not become an aid worker. Perhaps, someone would have taken your position and done a better job than you would—or perhaps you are especially suited to work as an aid worker since you have an unique ability to focus on making the organization more effective. Or it may be there is just too much uncertainty about what would happen if you do not work as an aid worker. What matters is that thinking about what would have happened otherwise is important in figuring out how to make the biggest difference. An effective altruist will not want to do what would have happened anyway (because the focus is on doing the most good) nor will they want to pass up an opportunity where they are especially suited to make an impact.

Finally, we should ask what the chances of success are and how good success would be. Here MacAskill introduces the notion of expected value. Calculating expected value concerns looking at all the outcomes, their value, and the probability of them obtaining. If we are considering flipping a coin and I get $2 when it comes up heads, but lose $1 when it comes up tails, then the expected value flipping the coin is 50¢ because (50% x $2) + (50% x -$1) = 50¢. What this shows is that sometimes working on something which has a low chance of occurring but which would be really good if it did occur can be better than doing good things which have a high-chance of occurring. For example, one might think that it is better to go into politics than to become a doctor even if one knows that it is likely that one could be a doctor but unlikely that one will be a successful politician.

With these five questions of effective altruism in hand, MacAskill goes on to evaluate particular charities, causes, and careers. He argues that we should tend to doubt the effectiveness of domestic charities. One chapter is entitled “The Moral Case for Sweatshop Goods.” He also doubts the efficacy of “green living,” suggesting that it is more effective to offset one’s greenhouse emissions by supporting effective organizations that work on reducing emissions in general.

Needless to say, there is disagreement in the effective altruist community about which causes are the most effective and important. MacAskill lays out the debate between causes that many effective altruists find promising: extreme poverty interventions, US criminal justice reform, international labor mobility, reducing factory farming, climate change interventions, and preventing or addressing global catastrophic risks. In evaluating these causes he focuses on three markers of effectiveness: scale (what is the magnitude of the problem?), neglectedness (is this cause in need of more resources than other causes?), and tractability (can I help make significant progress on this problem?). You might not agree with all of MacAskill’s analysis. For example, I doubt that US criminal justice reform is as tractable as extreme poverty interventions, but I look forward to future work on the topic. I am also hesitant of his analysis, cautious though it is, of two excellent organizations: Development Media International and GiveDirectly (he slightly favors DMI).

Central to MacAskill’s approach, and the approach of effective altruism in general, is the combination of critical thinking, open-mindedness, and compassion. Effective altruists care about doing good for others and because of this they want to figure out how to do the most good for others. This demands reasoning carefully about different causes and also demands an open-mind—dogma and ideology will not do. Hence, friendly and evidence-based disagreement with an eye toward progress is welcomed. Doing Good Better is a model for thinking about and making progress in these debates.

Because of this, I would happily recommend this book to anyone interested in making the world a better place. It is the best book of its sort.