News Release

Cooperation among strangers has increased since the 1950s

Findings offer hope for efforts to address global challenges

Peer-Reviewed Publication

American Psychological Association

Despite common concerns that the social fabric is fraying, cooperation among strangers has gradually increased in the U.S. since the 1950s, according to research published by the American Psychological Association.

“We were surprised by our findings that Americans became more cooperative over the last six decades because many people believe U.S. society is becoming less socially connected, less trusting and less committed to the common good,” said lead researcher Yu Kou, PhD, a professor of social psychology at Beijing Normal University. “Greater cooperation within and between societies may help us tackle global challenges, such as responses to pandemics, climate change and immigrant crises.”

The researchers analyzed 511 studies conducted in the United States between 1956 and 2017 with a total of more than 63,000 participants. Those studies included lab experiments measuring cooperation among strangers. The research was published online in Psychological Bulletin.
The study found a small, gradual increase in cooperation across the 61-year period, which the researchers said may be linked to notable shifts in U.S. society. The increase in cooperation was associated with increases in urbanization, societal wealth, income inequality and the number of people living alone. The study cannot prove those factors caused an increase in cooperation, only that there is a correlation.

Increased cooperation has been linked with market competitiveness and economic growth in prior research. As more people live in cities and on their own, they may be forced to cooperate with strangers, said study co-author Paul Van Lange, PhD, a professor of social psychology at Vrije Universiteit Amsterdam.

“It’s possible that people gradually learn to broaden their cooperation with friends and acquaintances to strangers, which is called for in more urban, anonymous societies,” Van Lange said. “U.S. society may have become more individualistic, but people have not.”

The studies that were analyzed occurred in lab settings primarily with college students as participants, so the findings may not be representative of real-life situations or of U.S. society as a whole. However, the researchers noted that prior studies have not found that levels of cooperation vary by gender or ethnicity in the U.S.

The study did not measure some other societal factors, such as levels of trust about strangers. Prior research has found a general decline in trust over several decades in the U.S.

“One intriguing implication of these findings is that while Americans’ cooperation has increased over time, their beliefs about others’ willingness to cooperate has actually declined,” the journal article stated.

Article: “Did Cooperation Among Strangers Decline in the United States? A Cross-Temporal Meta-Analysis of Social Dilemmas (1956-2017),” Yu Kou, PhD, Beijing Normal University, Mingliang Yuan, PhD, Anhui Agricultural University, Giuliana Spadaro, PhD, Shuxian Jin, PhD, Paul A. M. Van Lange, PhD, and Daniel Balliet, PhD, Vrije Universiteit Amsterdam, and Junhui Wu, PhD, University of Chinese Academy of Sciences. Psychological Bulletin, published online July 18, 2022.

Contact: Yu Kou, PhD, may be contacted at

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