The bystander effect, is a social psychological phenomenon in which individuals are less likely to offer help to a victim when other people are present. The greater the number of bystanders, the less likely it is that any one of them will help. Several factors contribute to the bystander effect, including ambiguity, cohesiveness and diffusion of responsibility. (Source: Wikipedia)

We regularly hear about incidents of molestation, physical abuse, bullying, kidnapping, trafficking and accidents,in public places where the victim was calling for help, pleading people to take action until it was too late.

If you’re not too hurt to call out for help, pick one person and direct your pleas to them. You’ll be more likely to get the aid you need.

How and why this may work is because of another psychological behaviour which goes hand in hand with ‘Bystander effect’. Namely, ‘Diffusion of responsibility’.

Diffusion of responsibility is a socio-psychological phenomenon whereby a person is less likely to take responsibility for action or inaction when others are present. Considered a form of attribution, the individual assumes that others either are responsible for taking action or have already done so. The phenomenon tends to occur in groups of people above a certain critical size and when responsibility is not explicitly assigned. It rarely occurs when the person is alone and diffusion increases with groups of three or more. (Source: Wikipedia)

Since Diffusion of responsibility rarely occurs when the person is alone, singling out one person in a crowd will have the same effect. The person is forced to take responsibility for any action or inaction on their part when particularly addressed to in a crowd. So, pleading to the guy in red jacket clearly indicating you are asking him for help will result in more chances of being helped than generally calling out to help to the entire crowd.

Here you got an experiment: