The economy's impact on giving to higher education isn't always what one might expect, according to a new study released by the National Bureau of Economic Research. Using a national sample of colleges and universities, the study found a positive correlation between average income and house values in a state and donations by the people who live in that state. However, the study also found an increase in donations -- especially for operating budgets -- when a university suffers a "negative endowment shock." The latter finding appears correlated to increased efforts by fund-raisers during such periods, and suggests that donors respond to such efforts. The study finds that these donations may be a form of "insurance" against endowment declines.