The most popular and widely researched explanation is that people experience a diffusion of responsibility when in the company of other bystanders. We don't help the person who is being assaulted in a busy street because we assume that someone else will.
But a new study in the Journal of Experimental Psychology: General provides evidence that there is much more to it than this – in particular, when deciding whether to help, we take into account the perspective of the other bystanders – whether they know that help is needed, whether they know that we know that help is needed, whether they know that we know they know that help is needed, and so on.
The researchers recruited over 2,000 volunteers on Amazon's Mechanical Turk survey website to take part in an economic game designed to simulate and simplify a bystander situation. In groups of two or five people, the participants were asked to imagine that they rented stalls at a market, earning $1 a day. Occasionally the market manager needed help from one merchant to get supplies and whoever helped would suffer a loss of half their earnings for that day. If no one helped, the manager would fine all merchants $1 for the day. Players knew the scenarios were fictional but that the money at stake was real.
In the loudspeaker condition, in which everyone knew that help was needed (and everyone knew that everyone else knew), the classic "diffusion of responsibility" finding was replicated – players were less likely to help when in a group of 5 than a group of 2. But in the other conditions, the outcomes were more complex and depended on participants' judgments about how likely it was that other people would help based on what they knew. For example, when participants knew that help was needed but that other merchants were ignorant, they were more likely to help. By contrast, when other merchants knew help was needed, and the other merchants didn't know that the participant knew help was needed, then the participant was less likely to offer to help.
Source material from BPS Research Digest