Tragedies like Hurricane Katrina, the Asian tsunami and the Sept. 11 attacks prompted billions of dollars in donations. But following an earthquake in Pakistan that killed 80,000... not so much. How much do Americans give to charitable causes? And why? Stephen Dubner, author of "Freakonomics," has numbers and answers. More: Dubner's Freakonomics blog
Takeaway facts: Americans give away the equivalent of 2 percent of the gross domestic product, but when Pakistan's earthquake struck (a few months after Katrina), Americans donated little: 5 cents a person in aid. And, new trends show Americans favoring environmental funding while shunning the arts.