Knowing how to get help when you need it is important, but more often we find ourselves in the position of the bystander rather than the victim. The next time you see someone in a crowd who looks like they may be in need of help, but no one seems to be helping them, say no to the bystander effect and respond as if you were alone with the victim.
As a final note -- diffusion of responsibility has consequences beyond times of crisis. You may witness this effect in action any time you are part of a group where no one is being held personally accountable for group outcomes. For example, when all of the employees in a large company are asked to help pay for a farewell gift for a coworker by putting a dollar in an envelope in the lunch room, the larger the company, the less likely it is that any one person will actually put in their dollar. Instilling a sense of responsibility in people, such as asking people to write their name on a list when they've put in their dollar, is also effective for getting help in these types of situations.
Have you ever been in this type of situation, either as the victim or the bystander? Was there a large crowd around?