Donation Gravity: An Analysis of Donations Made to the Red Cross through Amazon's Honor System
http://webword.com/moving/gravity.html

Rhodes, John S.
WebWord
2001

Abstract:

In light of recent terrorist attacks on the United States, Amazon.com set up a page to collect donations for the Red Cross. Over the course of about two and half days, I recorded the donation activity on that page. An analysis of the data revealed that the average amount of money donated by each person steadily increased (i.e., donation gravity). This manifestation of donation gravity is discussed, along with several usability ideas that can help you design a better online donation web page.