Are charitable gifts are complements or substitutes; are charitable fundraisers rivals? These questions are important to fundraisers, policymakers, and economic models of generosity. However, observational data lacks shocks that are clearly specific to giving to one charity; motivating experimental variation. We report on recent experimental work (our own and others’) from a variety of laboratory and field settings, under a range of design choices providing convergent validation. Most work presents simultaneous or proximately repeated donation opportunities to subjects, with noticeably varying “prices”, promotional information, and choice sets. Here, specific shocks strongly increase giving to the targeted charities, and lead to decreased giving to the remaining charities, particularly where charities serve similar goals. However, this may be driven by experimental demand and logical responses to obvious contrasts, which may not reflect real-world behavior. Our web-based experiments offer robustness to these critiques. We pay participants for completing two surveys unrelated to charitable giving, separated by multiple weeks. Some (all) participants have the opportunity to donate from their earnings to a single charity at the end of the first (second) survey. Between subjects, we vary the number of asks and the similarity of the first and second charities. The results offer further evidence of "expenditure substitution", but less support for the idea that similar charities crowd out each other more.

Please note: We are uploading a previous version of the paper; we aim to have a version integrating data from a range of recent experiments within the next few months.