The Bystander Effect describes how, as the amount of people who witness an event increases, the probability that each of them will act in response decreases.
Wikipedia provides this definition:
“The bystander effect is a social psychological phenomenon that refers to cases in which individuals do not offer any means of help to a victim when other people are present.”
In his book The Tipping Point, Malcolm Gladwell illustrates the Bystander Effect by describing the the now infamous 1964 stabbing of a young New Yorker by the name of Kitty Genovese (pictured).
“Genovese was chased by her assailant and attacked three times on the street, over the course of half an hour, as thirty-eight of her neighbors watched from their windows. During that time, however, none of the thirty eight witnesses called the police. The case provoked rounds of self-recrimination. It became symbolic of the cold and dehumanizing effects of urban life. Abe Rosenthal, who would later become editor of the New York Times, wrote in a book about the case:
“Nobody can say why the thirty-eight did not lift the phone while Miss Genovese was being attacked, since they cannot say themselves. It can be assumed, however, that their apathy was indeed one of the big-city variety. It is almost a matter of psychological survival, if one is surrounded and pressed by millions of people, to prevent them from constantly impinging on you, and the only way to do this is to ignore them as often as possible. Indifference to one’s neighbor and his troubles is a conditioned reflex in life in New York as it is in other big cities.”
This is the kind of environmental explanation that makes intuitive sense to us. The anonymity and alienation of big-city life makes people hard and unfeeling. The truth about Genovese, however, turns out to be a little more complicated — and more interesting. Two New York City psychologists — Bibb Latane of Columbia University and John Darley of New York University — subsequently con- ducted a series of studies to try to understand what they dubbed the “bystander problem.” They staged emergencies of one kind or another in different situations in order to see who would come and help. What they found, surprisingly, was that the one factor above all else that predicted helping behavior was how many witnesses there were to the event.
In one experiment, for example, Latane and Darley had a student alone in a room stage an epileptic fit. When there was just one person nest door, listening, that person rushed to the student’s aid 85 percent of the time. But when subjects thought that there were four others also overhearing the seizure, they came to the student’s aid only 31 percent of the time. In another experiment, people who saw smoke seeping out from under a doorway would report it 75 percent of the time when they were on their own, but the incident would be reported only 38 percent of the time when they were in a group. When people are in a group, in other words, responsibility for acting is diffused. They assume that someone else will make the call, or they assume that because no one else is acting, the apparent problem — the seizure-like sounds from the other room, the smoke from the door — isn’t really a problem. In the case of Kitty Genovese, then, social psychologists like Latane and Darley argue, the lesson is not that no one called despite the fact that thirty-eight people heard her scream; it’s that no one called because thirty-eight people heard her scream. Ironically, had she been attacked on a lonely street with just one witness, she might have lived.”