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.

中文翻译：

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陌生人之间的合作在美国下降了吗？社会困境的跨时间元分析（1956-2017）。

据推测，在过去的几十年里，陌生人之间的合作在美国有所下降，这是一个具有潜在深远社会影响的令人担忧的趋势。迄今为止，大多数支持合作减少的研究都依赖于自我报告措施或档案数据。在这里，我们利用了在涉及利益冲突（即社会困境）的情况下合作的实验研究历史。我们对 1956 年至 2017 年间进行的 511 项研究进行了元分析，其中包含 660 个独特样本和影响大小，涉及 63,342 名参与者，以测试在这些研究中观察到的平均合作水平是否随着时间的推移而下降。我们没有发现 61 年间合作减少的证据。相反，我们发现随着时间的推移合作略有增加。此外，一些社会指标（例如，收入不平等、社会财富、城市化水平和独居人口比例）在合作测量前 10 到 5 年测量，发现与合作呈正相关，这表明它们可能是合作增加的潜在社会基础。这些发现挑战了美国陌生人之间的社会资本和公民合作随着时间的推移而下降的观点，我们为未来的研究提供了方向，以了解合作增加的原因。