What is a bystander effect?

Bystander effect is when numerous people fail to help strangers in an emergency situation. Such as the case with Kitty Genovese, which happened in the year 1964 in the New York City. She was stabbed and raped on the street while walking home at night and even though she screamed for help, nobody helped her. Despite the fact that the neighbors heard her, it took them a long time to call the police and therefore Kitty Genovese did not survive.