Does Political Diversity Inhibit Blood Donations?

Does political diversity affect the prevalence of selfless behavior across a society? According to a recurrent finding from the study of social capital, ethnic diversity reduces prosocial behavior. We ask whether the same applies to partisan identity, by turning to a frequently used proxy for social capital: blood donations. The question is especially timely: the United States is currently experiencing its worst blood shortage in over a decade. Using survey results covering over 275,000 individuals in the US from 2010 to 2020, and a preregistered survey of an additional 3,500 respondents, we show that not all measures of social diversity have analogous effects on prosocial behavior. We find mixed evidence for a region's share of immigrants being linked to lower blood donation by US citizens, and no negative effect for racial diversity. By contrast, political diversity appears to be highly significant. Specifically, individuals are less likely to donate blood when their partisan position is farther from the mean political identity in their state or commuting zone, and when they perceive themselves to be political outliers in their community. Affective polarization is known to be a tax on social interaction with out-partisans; as we show, depending on an area's partisan makeup, it can also be a tax on prosocial behavior writ large.