Eight Symptoms of Groupthink

To make groupthink testable, Irving Janis devised eight symptoms indicative of groupthink (1977).

1. Illusions of invulnerability creating excessive optimism and encouraging risk taking.
2. Rationalizing warnings that might challenge the group's assumptions.
3. Unquestioned belief in the morality of the group, causing members to ignore the consequences of their actions.
4. Stereotyping those who are opposed to the group as weak, evil, biased, spiteful, impotent, or stupid.
5. Direct pressure to conform placed on any member who questions the group, couched in terms of "disloyalty".
6. Self-censorship of ideas that deviate from the apparent group consensus.
7. Illusions of unanimity among group members, silence is viewed as agreement.
8. Mind guards — self-appointed members who shield the group from dissenting information.

http://en.wikipedia.org/wiki/Groupthink#Symptoms_of_groupthink