Checking the Technical Notes
From the Technical Notes:
This is the aggregate data from the Internal Revenue Service on taxpayers who itemize and take a charitable deduction for their contributions. This information however, covers less than 30 percent of all US taxpayers, as over 70 percent take a standard deduction and do not itemize. Although the proportion of itemizing taxpayers is relatively small, their charitable deductions do represent about 60 percent of the total estimated charitable contributions in the United States (The Urban Institute, 2001)
[emphasis added]
Catalogue for Philanthropy. "National 2004 Generosity Index: Technical Notes." 2002 data [most current]. http://www.catalogueforphilanthropy.org/cfp/generosity_index/2004_us_notes.php [linked above].
Please note that there is no tabulation, valuation, or inclusion of personal time donated to any organization or institution.
We have approximately 70 volunteers who help us run our library. This index provides no way to count their contribution.
Cash isn't everything.