Many of our shortcuts concern other people: who is on our side, why people act as they do, and when to follow the crowd.

In-group bias

In-group bias is the tendency to favor members of our own group. In the early 1970s the social psychologist Henri Tajfel ran what are called minimal group experiments. British schoolboys were divided into groups on trivial grounds, such as whether they supposedly preferred paintings by Paul Klee or Wassily Kandinsky. They never met their group members, yet when dividing small rewards they favored their own group, sometimes even choosing to maximize the gap between groups over the total their own group received. The finding: people favor their own group even when groups are based on trivial criteria. Tajfel and John Turner later built this into social identity theory.

The fundamental attribution error

When someone cuts us off in traffic, we tend to think “What a jerk,” not “Maybe they are rushing to a hospital.” The fundamental attribution error, a name given by Lee Ross in 1977, is the tendency to explain other people's behavior by their character while underweighting the situation. In a 1967 study by Edward Jones and Victor Harris, readers saw essays praising or criticizing Fidel Castro. Even when told the writer had been assigned which side to argue, readers still assumed the writers held the views in their essays. We often do the reverse for ourselves, blaming circumstances for our own failings.

Conformity: Asch's lines

In the early 1950s Solomon Asch asked participants to say which of three lines matched a reference line, an easy task. The catch: the other people in the room were Asch's confederates, and on certain trials they all gave the same wrong answer. About one third of answers on those critical trials went along with the clearly wrong majority, and about three quarters of participants conformed at least once. About a quarter never did.

The most hopeful finding came from a variation: when just one other person gave the correct answer, conformity fell sharply. A single ally makes dissent much easier.

The bystander effect and updated evidence

In 1964 Kitty Genovese was murdered in New York, and a newspaper reported that 38 neighbors had watched without helping. Later investigation showed the story was badly exaggerated, but it inspired important research. In 1968 John Darley and Bibb Latané had students hear, over an intercom, someone who seemed to be having a seizure. Students who believed they were the only listener usually sought help quickly; those who believed four others were listening were much slower and less likely to act. They called this diffusion of responsibility: each person feels less responsible when others are present.

Newer evidence adds an important correction. A 2020 study by Richard Philpot and colleagues analyzed security camera footage of real public conflicts in three countries. In about nine of ten conflicts at least one bystander intervened, and the more bystanders there were, the more likely someone helped. Each individual may feel less responsible in a crowd, but a crowd as a whole often provides help. The idea that people in groups usually do nothing is a myth.

The halo effect

In 1920 the psychologist Edward Thorndike noticed that army officers rating their soldiers gave suspiciously similar scores for physique, intelligence, leadership and character. He named this the halo effect: one positive trait coloring our judgment of a person's other traits. Attractive, confident or well-spoken people are often assumed to be more competent and honest than the evidence supports.

Worked example: when someone collapses

A man collapses on a busy train platform. Dozens of people are nearby. What happens next, and how can research help?

The risks. Each person may assume someone else is already helping or has called for help: diffusion of responsibility. People also look around to see how others are reacting. If everyone looks calm because everyone is checking everyone else, each concludes it may not be an emergency. This is called pluralistic ignorance.

The good news. The 2020 security camera study suggests that in real emergencies someone usually does step in, and that a larger crowd raises the odds that at least one person acts. Once one person moves, others often follow.

What you can do.

• Be the first to define the situation out loud: “This man needs help.” That breaks pluralistic ignorance.
• Give specific tasks to specific people: “You in the green jacket, please call emergency services. You, please find a staff member.” That cuts through diffusion of responsibility, much as a single ally broke the spell in Asch's experiments.
• If you are the one who needs help, do the same: pick out one person and ask them directly.

Avoiding the attribution error. Later, a commuter says the people who stood back were heartless. The fundamental attribution error is at work: their hesitation may reflect uncertainty, lack of training or not seeing what happened, not bad character. Training and clear roles change behavior more than blame does.