Why the parts are better (or worse) than the whole: the unique-attributes hypothesis.

People tend to rate members of a positive group (e.g., best friends) as superior to the average of that group and members of a negative group (e.g., worst enemies) as inferior to the average of that group. Five experiments tested a new theoretical account of these nonselective superiority and inferiority biases. According to this account, a member's unique attribute (the dimension distinguishing that member positively or negatively from other group members) is used as the standard for comparing that member with other group members. The experimental results supported this hypothesis. When participants compared a randomly selected popular or unpopular vacation destination with other destinations, the target destination's unique attribute was more accessible than its nonunique attributes (Experiments 1-4), and a popular destination was judged less above average if one of its nonunique attributes was the salient comparison standard (Experiment 4). In addition, the unique attribute was used as the comparison standard for evaluating novel stimuli (Experiment 5). Alternative accounts and implications for general comparison processes are discussed.