Final answer:
Diener and his colleagues conducted a study on trick-or-treating on Halloween night to examine deindividuation and its effect on children's behavior.
Step-by-step explanation:
The primary reason why Diener and his colleagues conducted a study in 1976 on trick-or-treating on Halloween night was to examine the concept of deindividuation. Deindividuation refers to situations where a person feels anonymous, leading to a reduction in accountability and sense of self. In this specific study, they were interested in how being in a group and not being identified would affect children's behavior.
The correct answer to the question is option d) Children who were in a group and not identified took more candy than they were allowed, but only when they were with other children who were alone and could be identified. The study found that children who were in a group and not identified were more likely to engage in deviant behavior when they were with other children who were alone and could be identified. This supports the idea that deindividuation can lead to increased antisocial behavior.