"There are very few instances, except possibly in religious giving, where people give out of guilt," she said.
Brown noted that in this global economy, residents of developed countries tend to have relatively high incomes. But she points out that while incomes might be low in many parts of the third world, so are prices for many goods.
"People with very low income, in some countries, can live very well because their income goes further than ours," Brown said. Any comparison of world incomes, she said, should also factor in so-called purchasing parity.
Not all families give to charity, but of those who do, Brown said, the average is 3 percent of their income. She said that rich, poor and middle class families who do give all tend to give the same percent of income.
The majority of giving comes from individuals, said Naomi Levine, the executive director of New York University's George H. Heyman Jr. Center for Philanthropy and Fundraising. Only nine to 10 percent of philanthropic donations come from corporations.
"There are many reasons why people give," Levine said. "Some people are genuinely altruistic -- they feel good when they help somebody and make a gift."
Generally, individuals may be inclined to donate if they believe in the organization or institution, Levine said.
Donating toward a cause that fights global poverty -- a seemingly distant experience for many Americans -- is probably driven by an emotional experience such as visiting a developing nation or having read about a poor country, said Richard Gelles, dean of the University of Pennsylvania's School of Social Policy and Practice.
Or, it could be driven by the altruistic belief of giving back toward a cause you support because you are in a position to do so, he said.
Upon informing a user of his or her wealth relative to the global population, the site provides a handful of examples of how much a donation can accomplish. "All you have to do is make a choice," the Web site says.
While guilt might convince some individuals to give small donations, it cannot explain the majority of transformative donations, he said.
"Getting someone to give is only half the battle," Gelles said. "Getting them to give intelligently and effectively -- that's the other half."
According to the site, a donation of $73 could buy a new mobile health clinic for AIDS orphans in Uganda.
Claims such as these, which point to specific ways a donation can help others, are very effective.
"Concreteness, tangibility for most philanthropists is key," Gelles said. "You can get more people to give money for bed nets to prevent malaria than to invest in research to prevent malaria."
"The tangibility of the bed nets and the number of people who have bed nets and are protected from malaria, even if it's a tiny number, seems more tangibly effective than research that 10 years down the road might save 100 million people."
Individuals from modest backgrounds who consider themselves philanthropic give between two and 10 percent of their gross income to charity, Gelles said. Other factors that encourage philanthropy include being asked to donate to a cause by a good friend (sometimes known as "reciprocal philanthropy"), adherence to religious mandates to give back and personal experience associated with the cause. Looking to benefit from tax deductions is not a driving factor behind personal philanthropy, Levine said.