Did cooperation among strangers decline in the United States? A cross-temporal meta-analysis of social dilemmas (1956–2017).

Public Significance Statement This meta-analysis reveals that Americans' level of cooperation among strangers has increased over the 61-year period from 1956 to 2017. This finding challenges the idea that social capital and norms of cooperation have declined in the American society over time. Changes in American society support greater cooperation among strangers, which could underlie an ability for Americans to cooperate to solve present and future challenges (e.g., solutions to climate change, pandemics, and sustainable resource consumption). Cooperation among strangers has been hypothesized to have declined in the United States over the past several decades, an alarming trend that has potential far-reaching societal consequences. To date, most research that supports a decline in cooperation has relied on self-report measures or archival data. Here, we utilize the history of experimental research on cooperation in situations involving conflicting interests (i.e., social dilemmas). We meta-analyzed 511 studies conducted between 1956 and 2017 with 660 unique samples and effect sizes involving 63,342 participants to test whether the average level of cooperation observed in these studies had declined over time. We found no evidence for a decline in cooperation over the 61-year period. Instead, we found a slight increase in cooperation over time. In addition, some societal indicators (e.g., income inequality, societal wealth, urbanization level, and percentage of people living alone) measured 10 to 5 years prior to measures of cooperation were found to be positively associated with cooperation, suggesting that they may be potential societal underpinnings of increases in cooperation. These findings challenge the idea that social capital and civic cooperation among strangers have declined in the United States over time, and we offer directions for future research to understand causes of an increase in cooperation.