Are you less likely to get help when lots of people are watching?

In the lab, yes: each person is less likely to step in when others are around. On real streets, though, someone usually does help, and a bigger crowd makes it more likely that at least one person will. That tension sits at the heart of the bystander effect, the idea that we help less when other people are present.

The idea was born from a story. In 1964 Kitty Genovese, a 28-year-old bartender, was murdered outside her apartment in Queens, New York. Two weeks later a newspaper claimed that dozens of neighbours had seen or heard the attack and done nothing. That account turned out to be badly exaggerated. Many neighbours thought they were hearing lovers or drunks quarrelling, two people did call the police, and her friend Sophia Farrar held her in her arms, whispering that help was on the way.

Still, the story inspired real experiments, and their results were striking. In one, 70 percent of people sitting alone went to help a woman they thought had fallen and hurt herself, but only 40 percent did when sitting with a stranger. In groups, people watch each other: if nobody reacts, the situation must not be an emergency. And each person assumes someone else will take charge.

But a 2019 study of more than 200 real surveillance videos found that in over 90 percent of public conflicts, at least one bystander stepped in. Each of us may hesitate in a crowd, yet a crowd contains more potential helpers.