Deindividuation Theory of
• Deindividuation – to lose one’s sense of
individuality and identity.
• Can occur in 2 main ways –
– Becoming part of a crowd
– Identifying with a particular role ( often aided by
wearing uniform or mask)
Can be used to explain aggression which occurs when in a group.
• Le Bon (1895) – individuals are more likely to
behave in aggressive manner when part of a
large anonymous group.
• A collective mindset is created and the group
can become a ‘mob’.
Individuals feel less
identifiable in a group, so the
normal constraints that
prevent aggressive behaviour
may be lost. The shared
responsibility for action
reduces individual guilt.
Diener (1980)
• Deindividuation occurs
when self awareness is
blocked by
environmental events.
• Critical factors include :
– Strong feelings of group
The deindividuated individual is
trapped in the moment, perception of
time is distorted and they are unable to – Increased levels of
consider consequences.
– Focus on external events
– Feeling of anonymity
Diener cont.
Increased arousal
Strong group feelings
External focus
Sense of anonymity
Reduced self awareness
Prentice-Dunn & Rogers (1982)
• Modified Diener’s theory to distinguish between:
– Public self awareness - concern over the impression of
yourself you are presenting to others when you are aware of
being judged.
– Private self awareness – your sense of self, consisting of
thoughts, feelings, values and internal standards of behaviour.
Reduction in either can result in aggressive
behaviour, but only reductions in private self
awareness can lead to genuine
• Zimbardo (1973) Stanford Prison experiment
You have 30 minutes to research and
outline this classic experiment and apply
deindividuation theory to the guards
aggressive behaviour.
Zimbardo (1969)
Is it relevant
that all the
were women?
Explored deindividuation in female undergraduates.
Group 1 dressed in white lab coats with hoods over their faces
Group 2 wore large name tags.
All pps observed a woman being interviewed and evaluated her
performance by administering electric shocks.
Condition 1 – pleasant interviewee, condition 2 – obnoxious
Group 2 shocked the obnoxious interviewee more than the
pleasant one
Group 1 (deindividuated) shocked both interviewees equally.
Zimbardo concluded that deindividuation increased aggression,
making it indiscriminate and not at all influenced by individual
Ellison et al (1995)
• Field experiment – drivers of convertibles with tops up
beeped more than those with tops down.
• Driving simulation exp’t with 289 psych student pps.
• Measured aggressive driving (speed, jumping red lights,
collisions etc.) in tops up / tops down conditions.
• More aggression shown in tops up(anonymous)
Is this experiment
high or low in
ecological validity?
Rehm et al (1987)
• Aggression in handball
• Deindividuation was created
by giving one team orange shirts, whilst other team
wore own clothes.
• In boy teams, uniformed teams were more aggressive
than non-uniform.
• In girl teams, no differences found.
• Researchers concluded that uniform > loss of
Is there an alternative
individuality > deindividuation.
explanation? How can the
gender difference be
Cross cultural evidence
• Watson (1973) – 24 cultures.
• Warriors in face and body paint more
likely to kill, mutilate and torture
captured prisoners.
• Silke (2003) – violent assaults in
Northern Ireland.
• 206 / 500 cases carried out by offenders
wearing masks or disguises.
•Anonymous attackers were more prolific
and inflicted more serious physical
injuries than identifiable attackers.

Deindividuation Theory of Aggression