Working-age Americans who make $50,000 to $100,000 a year are two to six times more generous in the share of their investment assets that they give to charity than those Americans who make more than $10 million, a pioneering study of federal tax data shows.

The least generous of all working-age Americans in 2003, the latest year for which Internal Revenue Service data is available, were among the young and prosperous -- the 285 taxpayers age 35 and under who made more than $10 million -- and the 18,600 taxpayers making $500,000 to $1 million. The top group had on average $101 million of investment assets while the other group had on average $2.4 million of investment assets.

On average these two groups made charitable gifts equal to 0.4 percent of their assets, while people the same age who made $50,000 to $100,000 gave gifts equal to more than 2.5 percent of their investment assets, six times that of their far wealthier peers.

Investment assets measures the value of stocks, bonds and other investments assets held in the tax system. Excluded from this are retirement accounts, which are generally held outside the tax system, personal property like furniture and art and equity in homes.