Definition: Diffusion of Responsibility
Diffusion of Responsibility is the phenomenon where: "each bystander's sense of responsibility to help decreases as the number of witnesses increases" (Psychology Glossary). In other words, people are less likely to take responsibility or take action in groups with a large amount of people present.

The concept Diffusion of Responsibility can help explain other psychology concepts such as:
-The Bystander Effect, where people do not offer help to others in an emergency when other people are around.
-Deindividuation, where people can experience a loss of self awareness and ability to apprehend oneself in a group situation
-Groupthink, where a group makes "faulty decisions" as a result of pressure from other members of the group (psyr)

Darley and Lanté (1968):
-Hypothesis: bystanders are apathetic because they feel that their individual responsibility is reduced in a large group.
-Experiment: Subjects thought they could hear someone having a seizure in another room. Some subjects were told they were one of two subjects, others were told they were one of six subjects in the experiment.
-Results: With the two-person condition, 85% of subjects took action in response to the seizure. With the six-person condition, only 31% of the subjects responded. This supports the hypothesis of the experiment.

Lanté and Darley (1970):
-Experiment: A fake robbery was set up at a liquor store. When the clerk went away, two men stole beer from the store.
-Results: When customers were alone, 65% of them reported the robbery. When customers were in a group, 56% of them reported the incident.
-Conclusion: "'The point of the experiment was to see if other customers (who thought the robbery was genuine) would mention it to the clerk, when the clerk came back to the front of the store...This effect was quite a bit smaller than the diffusion of responsibility effect in the laboratory studies, although it was in the predicted direction' (Lanté and Darley, 1970)"

Through additional studies that can be found at the link below, it has been discovered that: characterisitics of the victim, previous personal contact, and a combination of these two variables can be a factor in bystander apathy and Diffusion of Responsibility.
Click here to learn more about the research done on Diffusion of Responsibility:

Questions About the Studies (answer after visiting the website above)
1)Which experiments supported the theory of Diffusion of Responsibility?

2)What was Kelmen's Warning? How does this relate to flawed experiemnts?
3)How does Diffusion of Responsibility relate to the Bystander Effect? How do these experiments show this relationship?
Example 1: The Smoked Filled Room Study
This experiment is similar to the experiment conducted by Darley and Lanté. Subjects are put next to a smoking room. Notice the time difference in subject's reactions when the subject is alone vs when the subject is surrounded by a group of people.

Example 2: The Murder of Kitty Genovese
A woman named Kitty Genovese was stabbed to death on a street in New York City. It was later discovered that 38 people witnessed the attack. Not one of them made an attempt to save Genovese from her attackers. Each witnesse believed that another person would intervene, or at least call the police. Because everyone shared this belief, no one aided Genovese.
To find out more about the murder of Kitty Genovese, follow this link:

Example 3: NHS Culture
Diffusion of Responsibility can happen at Needham High School in situations where students find themselves in large groups (cafeteria, between classes, etc). For example, if someone falls or drops his or her bag in the hallway between classes, students would not be likely to assist that person in need. Some people may just not notice. Others may notice, but believe that someone else will be there to lend assistance later.

Works Cited

Darley Bibb Latane, John M. “Bystander Intervention in Emergencies: Diffusion of Responsibility .” Wadsworth. N.p., n.d. Web. 29 Mar. 2012. <‌psychology_d/‌templates/‌student_resources/‌0155060678_rathus/‌ps/‌ps19.html>.

Dewey, Russell A. “Diffusion of Responsibility.” Psych Web. N.p., n.d. Web. 29 Mar. 2012. <‌ch15_social/‌diffusion_of_responsibility.html>.

Psychology Glossary. N.p., n.d. Web. 29 Mar. 2012. <‌cms/‌glossary/‌glossary-d/‌diffusion-of-responsibility.html>.

The Smoke Filled Room Study. Youtube. N.p., n.d. Web. 29 Mar. 2012. <‌watch?v=KE5YwN4NW5o>.

“What is Groupthink.” Psychologists for Social Responsibility. N.p., n.d. Web. 29 Mar. 2012. <‌about/‌pubs_resources/‌groupthink%20overview.htm>.