Groupthink is related to the bandwagon effect - the tendency to do (or believe) things because many other people do (or believe) the same.

Illusion of control - the tendency for human beings to believe they can control or at least influence outcomes that they clearly cannot.

Selective perception - the tendency for expectations to affect perception.

Halo effect - the tendency for a person's positive or negative traits to "spill over" from one area of their personality to another in others' perceptions of them.

CowboyNeal option bias - the tendency for a person to vote for the joke CowboyNeal poll option.