The percentage of personal income Americans give away each year has remained stable at 1.9 percent since the mid-1970s -- even while tax rates have fluctuated wildly. That is one conclusion of the latest National Survey on Philanthropy and Civic Renewal.

Here are a few of the key findings:

• Individuals give $110 billion a year to charity -- 10 times the amount given by all the foundations in America combined.

• Ninety-three million Americans do charitable volunteer work, averaging four hours a week each.

• About 80 percent of giving comes from people with incomes of less than $100,000 a year.

• Among the 1,010 randomly selected adults who were surveyed, the median amount given to charity was $500 annually.

Six out of 10 Americans report volunteering their time to some civic or charity endeavor within the past year. Nearly one in 10 has done fundraising or recruited others to volunteer.

Overall, 20 percent of those surveyed think volunteering time to community service is "absolutely essential," and 25 percent believe it is their "obligation as an American." But more than half, or 54 percent, feel it is "entirely a matter of personal preference."

Seventy-nine percent said they would prefer to remain anonymous when they contribute money or volunteer time. Only 8 percent said they would prefer people to know about their charity.