The relation between income and donations as a proportion of income revisited: literature review and empirical application

Previous research addressing the relation between income and donations as a proportion of income has revealed predominantly inconsistent results. In this article, we argue that this can partly be explained by the great variance of methodological approaches. Providing a literature review covering 26 studies, we systematically identify how methodological issues such as data, variables, and methods have affected former findings. In addition, we apply different methodological approaches to Austrian income tax data (n = 20,000), demonstrating how different methods lead to a variation in results. Overall, we show that existing studies are hardly comparable as their designs vary strongly. We point out that it is particularly important to use samples with sufficient cases of all income groups and methods that adequately account for the non-linear relation between the two variables, not restricting it to a U-shape. Our findings enable a better understanding and interpretation of diverging findings in philanthropic research.