bystander effect
a phenomenon in which people fail to offer needed help in emergencies, especially when other people are present in the same setting. Studies of this tendency, initially described in response to well-publicized failures of bystanders to render aid in emergencies, have identified a number of psychological and interpersonal processes that inhibit helping, including misinterpreting other people’s lack of response as an indication that help is not needed, confusion of responsibility, and diffusion of responsibility.