Most donors say they want to "help people". If that's true, they should try to distribute their resources to help people as much as possible. If you are to "love your neighbor as yourself", then you should be as careful in maximizing the benefit to others when donating to charity as you would be in maximizing the benefit to yourself when choosing purchases for a polar trek.

There is only one best charity: the one that helps the most people the greatest amount per dollar.

This is vague, and it is up to you to decide whether a charity that raises forty children's marks by one letter grade for $100 helps people more or less than one that prevents one fatal case of tuberculosis per $100.

GiveWell.org, a site which collects and interprets data on the effectiveness of charities can help you make these decisions. For instance, data collected from the site predicts that antimalarial drugs save one child from malaria per $5,000 worth of medicine, but insecticide-treated bed nets save one child from malaria per $500 worth of netting. If you want to save children, donating bed nets instead of antimalarial drugs is the objectively right answer, the same way buying a $500 TV instead of an identical TV that costs $5,000 is the right answer.

It is important to be rational about charity for the same reason it is important to be rational about Arctic exploration: it requires the same awareness of opportunity costs and the same hard-headed commitment to investigating efficient use of resources, and it may well be a matter of life and death.

Read the full article Efficient Charity by Scott Alexander at effectivealtruism.org