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Peter Singer is the Ira W. DeCamp professor of bioethics at Princeton University. His books include “Animal Liberation,” “Practical Ethics” and “The Life You Can Save.”

Many Americans give to charity, but few do any research on the charities to which they give. Much of that is what psychologists call “warm glow” giving — when people who are comfortably off give $10 or $20 to a charity, it’s more likely because it makes them feel better than because they are serious about helping the charity’s cause.

Meeting social expectations drives another segment of giving. We respond to what our church, mosque or synagogue expects from us, or to what our college friends tell us they are giving to the alma mater. If someone we love died from breast cancer, most people will nod approvingly if we buy a pink ribbon. Few will ask how much money is already going to breast cancer research or whether our donation would be more worthwhile if directed elsewhere.

Today, effective altruists are asking these tough questions. We should, they say, give to the charity that will do the most good with our dollars. But some people balk at that idea. With so many different causes, how can we say which does the most good? Is it even possible to compare the different benefits we might bring about, when our donations could go to charities with objectives as varied as preventing diseases such as malaria that sicken and kill millions of children in developing countries, reducing the suffering of animals, helping the homeless in our local communities or building a new opera house?

[See more of our new Opinions blog: “In Theory"]

Many people think that we can’t argue about our fundamental values. In the language of the day, it just depends on your “passion.” But passion is a poor guide. Anti-vaccinators can be just as passionate as people working for human rights.

There is, however, a rational basis for ethics in the idea of transcending our particular local or tribal interests and taking a universal perspective. Absent the evidence that there is greater potential for happiness or misery in one person’s life than in another’s, we should be equally concerned that every person — and every sentient being — is able to avoid suffering and find as much happiness and fulfillment they can.

From this basic principle, it follows that we should focus our charitable donations on people in extreme poverty in developing countries. That’s because for any given sum, we can do more good by helping those in greatest need. We can, for instance, save the lives of more infants in developing countries than we can save in the United States or any other developed nation. That’s because infants in the United States rarely die from diseases that we can inexpensively prevent or cure, whereas infants in developing countries still do.

Similarly, if we aim to prevent suffering rather than premature death, helping the homeless in the United States is likely to prove more costly than options for preventing suffering in developing countries, for example by repairing an obstetric fistula in a young woman who, without a surgery that by U.S. standards is extraordinarily cheap, will be a pariah for the rest of her life because she is unable to keep herself clean.

[An introduction to our new blog “In Theory"]

Most of us agree that the suffering of animals matters too, but it is much more difficult to compare the suffering of animals with human suffering. What is it like to be a pig crowded together with others in a factory farm, and how does that compare with various forms of preventable human suffering? I don’t know the answer, but if reducing the suffering of animals is much less expensive than reducing human suffering, then that will start to seem a defensible option, especially since reducing meat consumption will also reduce greenhouse gases and have other environmental and health benefits.

But why, you may ask, does preventing suffering trump, say, excellence in opera production?

Ask yourself how important excellence in opera would be to you if the health of your family was at risk. You wouldn’t have to think very hard. There are some things that we cannot really consider priorities until we have met all our more urgent needs; but from a universal perspective, our urgent needs are of no greater significance than the urgent needs of others.  If we are willing to sacrifice the highest levels of excellence in opera for the health of those we love, but not for those who are far away, we are not doing the most good we can.

Read more about this topic:

Christine Emba: Effective Altruism: a primer

Catherine Hollander: How do you quantify ‘good’?

Jeremy Beer: Traditional charity fosters love. Effective altruism doesn’t. 

William Schambra: Most Americans aren’t “efficient” philanthropists. That’s a good thing.

William MacAskill: Working for a hedge fund could be the most charitable thing you do.

Gary P. Steuer: Could effective altruism destroy the arts?