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Alan Wolfe, a political science professor at Boston College and head of the school’s Boisi Center for Religion and American Public Life, told the Associated Press that people in less-religious states are willing to give by paying higher taxes, and thereby funding more government programs to care for the poor and sick.

They “view the tax money they’re paying not as something that’s forced upon them, but as a recognition that they belong with everyone else, that they’re citizens in the common good,” he said. “I think people here believe that when they pay their taxes, they’re being altruistic.”

While religion plays a role, basic questions about the role of government also have a tremendous impact in determining how much someone gives, Mr. Grieboski said.

“People who lean to the political left will rely on the government and pay higher taxes to manage social needs,” he said. “People who lean conservative will rely more on the individual and on religious institutions and civil society nonprofits to handle those needs.”

Indeed, President Obama and Vice President Joseph R. Biden have pushed tax increases during campaign stops by calling them patriotic acts.

“It’s time to be patriotic … time to jump in, time to be part of the deal, time to help get America out of the rut,” Mr. Biden said about higher taxes on wealthier Americans during a 2008 interview with ABC News.

The survey also reinforced a counterintuitive phenomenon: Those who can most afford to give don’t do it as often.

Households that earn $50,000 to $75,000 gave an average of 7.6 percent of their income to charity in 2008, compared with 4.2 percent for those who make $100,000 or more. That effect holds true for tithing and for donations to secular groups.

Those who live in wealthy neighborhoods also are likely to be less charitable, regardless of income.

Those making more than $200,000 per year gave 4.2 percent of their money to charity, but when such high earners account for at least 40 percent of all taxpayers in a given ZIP code, the donation rate falls precipitously to 2.8 percent for that area.

“The wealthiest Americans are the ones who give a smaller portion of their disposable income to charity. It’s the middle-class Americans who give the larger portions,” Mr. Schneck said.

As for why, there is no clear answer.

“It’s a question people who study philanthropies have been trying to figure out for years,” he said.