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The bystander effect matters because it predicts, counter-intuitively, that a person in danger is often less likely to receive help the more other people are present. This has direct implications for how emergencies should be handled in public and clinical settings. For example, imagine someone collapsing on a busy street, with dozens of people nearby, each individual may assume someone else will help or has already called for help, and as a result no one does. This is driven mainly by two mechanisms. Diffusion of responsibility means each bystander feels less personal responsibility to act as the number of other bystanders increases. Pluralistic ignorance means each bystander looks to others' apparent calm to judge whether the situation is really an emergency, and everyone appears calm because everyone else is also just watching.

Latané and Darley's five-step model describes the sequence a bystander must complete before helping: noticing the event, interpreting it as an emergency, assuming personal responsibility, knowing how to help, and deciding to act. A failure at any single step results in no help being given. Picture a crowd witnessing someone collapse: several people notice (step 1) but each assumes it is not serious because no one else looks concerned (failure at step 2, pluralistic ignorance), so no one moves to step 3. The single most effective way to overcome the bystander effect is to single out one specific bystander directly, e.g. 'you in the blue coat, call an ambulance'. This assigns personal responsibility and bypasses diffusion of responsibility directly.

• What is now known about the 1964 murder case that prompted bystander research?
• In Latané and Darley's model, which step comes first before a bystander can help?
• What do modern studies of real recorded public conflicts show about bystanders?

• Bystander effect, less likely to help as more bystanders are present, unlike social loafing, which is reduced individual effort specifically on a shared group task, not a shared observed emergency.
• Diffusion of responsibility, each bystander feels less personally responsible as numbers increase, whereas pluralistic ignorance is misjudging an emergency as a non-emergency because everyone else appears calm.
• Singling out a specific bystander, assigns personal responsibility directly, rather than a general appeal to the crowd, which allows diffusion of responsibility to persist.

• Some but not all witnesses acted.
• Non-intervention was the exception rather than the rule in these data.
• The murder was real, and only the reporting was inaccurate.
• The case prompted the entire Latané and Darley research programme.
• The victim died as a result of the attack.

• Name the learning, social or research principle being tested before reading the options.
• Identify the antecedent, behaviour, consequence or cognitive process in the vignette.
• Compare the direction of effect with the nearest competing principle.
• Apply the same rule to a new example to confirm that the answer transfers.