Dunn and her colleagues found that the higher the percentage of their windfall workers spent on others, the happier they were, an effect that still existed when statistically controlling for relevant variables such prior happiness, income amount, and bonus size. What’s more, the data revealed that how the employees spent their money was a better predictor of their happiness than the size of the bonus itself.
For more, see this
article by Noah Goldstein reporting the work by Dunn, Aknin, and Norton over on Bob Cialdini's website.
