Implicit biases are harder to change in big cities than in small cities

Every human has implicit biases, or involuntary associations about members of different social groups. But these biases are not fixed. Rather, they’re malleable reflections of our everyday experiences.
It’s harder to change the biases of people living in big cities, with millions of people, however, than it is to change the biases of people living in small cities, with around 150,000 residents, a new study shows. This is “the first strong proof of how contextual biases are,” says Andrew Stier, a Complexity Postdoctoral Fellow at the Santa Fe Institute who performed the work.
Stier analyzed the results of an online test measuring biases for millions of study participants from cities across the United States. He also gave 1,150 study participants from cities across the United States the same test. After, they read a short story in which a member of a group they were biased against (or an “outgroup”) helped them out of a stressful situation, like facing a terminal illness or homelessness. Then they took the test again.
While the story reduced participants’ biases in every city, regardless of population size, the length of the impact varied. Stier asked participants to re-take the implicit bias test in the days following the intervention. In small cities, the intervention lasted until the end of the study, nine days later. In large cities, on the other hand, the effect faded within twenty-four hours.
Stier attributes this difference to two qualities of big city life: First, residents are likely to interact with outgroup members frequently, which means one additional experience doesn’t necessarily make a big difference. In small cities, on the other hand, the intervention provided in the study might be the first experience a study participant has ever had with a member of the outgroup, so it could shift their opinion quite a lot.
Second, big-city dwellers have a constant stream of information about other groups coming at them in the forms of interpersonal interactions, advertisements, TVs playing in restaurants, people listening to music, “let alone what we see on our phones,” Stier says. Small cities, on the other hand, tend to be quieter. So it makes sense that it will take a heftier intervention to shift the biases of people in big cities. In a big city, the intervention will get diluted by all the other information people get in a day.
Companies use implicit bias interventions to avoid making biased hiring decisions. For this approach to be successful, they should consider the size of the city they’re based in, Stier says. Big-city companies might be wise to host the intervention directly before making the decision because the effect will wane quickly. “That’s a pretty big reframing of how we think about the design of these interventions,” he says.
Read the paper "Implicit biases change more slowly in larger cities" in PNAS (August 6, 2026). DOI: 10.1073/pnas.2514189123

* Study participants measured implicit biases across cities in the United States.
* The study involved 1,150 participants from various cities.
* Participants read a story where an outgroup member helped them with a stressful situation.
* Bias was measured before and after this intervention.
* Intervention lasted nine days in small cities and twenty-four hours in large cities.
* The effect of the intervention varied based on city size, not just the intervention itself.
* Large city dwellers interact frequently with outgroup members.
* Large city dwellers receive a constant stream of external information regarding other groups.

Implicit biases are malleable reflections of everyday experiences, and the context in which these experiences occur significantly affects their malleability. A study found that changing implicit biases is easier in small cities with fewer residents than in large metropolitan areas. This difference was observed when participants experienced a social intervention involving an outgroup member helping them through a stressful situation. In small cities, this experience had a stronger impact on reducing biases, potentially because it represented a more significant novel interaction for the participants. In contrast, large city dwellers, due to constant exposure to interpersonal interactions and information streams, experienced a weaker effect, as new experiences are diluted by a continuous stream of external stimuli.

The finding suggests that the environment structures the pathway for cognitive change. The difference in impact is rooted in the density of social exposure and information flow inherent to urban environments. In large cities, continuous interaction means single events are subsumed into a broader context, requiring a more extensive intervention to shift deeply ingrained associations. Conversely, the novelty of the experience in smaller settings allows a specific event to serve as a more potent catalyst for reevaluation. This speaks to the tension between constant environmental conditioning and the capacity for individual cognitive reshaping. For organizational applications like bias intervention, this implies that success depends on recognizing whether context allows for rapid or protracted impact, shifting design away from uniform application toward context-sensitive delivery. What assumptions about the "baseline" experience of city life are we implicitly accepting when designing solutions meant to address implicit bias?

Implicit biases are harder to change in big cities than in small cities

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Implicit biases are harder to change in big cities than in small cities

Facts Only

Executive Summary

Full Take