In research on giving, methodology is destiny. The volume of donations estimated from sample surveys strongly depends on the length of the questionnaire used to measure giving. By comparing two giving surveys from the Netherlands, the authors show that a short questionnaire on giving not only underestimates the volume of giving but also biases the effects of predictors of giving. Specifically, they find that a very short module leads to an underestimation of the effects of predictors of giving on the amount donated but an overestimation of their effects on the probability of charitable giving. Short survey modules may lead researchers to falsely reject or accept hypotheses on determinants of giving due to underreporting of donations. © 2006 Association for Research on Nonprofit Organizations and Voluntary Action.