Giving USA’s annual estimates are based on original surveys of organizations and econometric studies using tax data, government estimates for economic indicators, and information from other research institutions. Sources of data used in the estimates include the Internal Revenue Service, U.S. Department of the Treasury, Bureau of Economic Analysis, Foundation Center, INDEPENDENT SECTOR, Council for Aid to Education, National Center for Charitable Statistics at the Urban Institute, and National Council of Churches of Christ.

Giving USA estimates the percentage of change in giving to subsectors (health, arts, education, religion, etc.). Except for giving to religion and giving to foundations, these estimates are developed by the Center on Philanthropy at Indiana University based on a survey conducted by Walker Information Group. Rates of change for 2005 are based on responses from 803 organizations.

With disaster giving included, Giving USA found total growth of 5.7 percent when estimating the dollar amount of gifts received at organizations. When estimating giving by adding together the results of the four sources of contributions, Giving USA found a growth in giving of 6.1 percent.

The estimates for the sources of giving are developed separately from the estimate of the receipts by type of recipient. The fact that the two entirely different methods come within 0.5 percentage points is one measure used by the Giving USA Advisory Council to evaluate the results prior to their release.