The term "diversification bias" refers to the tendency for people to take more variety when choosing several items simultaneously than when choosing them sequentially. In this article, we investigate whether this really is a bias by measuring evaluations of sets chosen simultaneously or sequentially. In Experiment 1 participants made two choices between audio tracks for consecutive consumption. Participants liked low-variety sets most and were more likely to choose high-variety sets in simultaneous choice. In Experiment 2 participants chose between three gambles which varied in the probability of winning and their expected value. Again, simultaneous choices seemed worse than sequential ones: The simultaneous-choice groups took far more low expected value gambles than did sequential-choice subjects and rated their enjoyment as lower. We conclude that simultaneous choice often leads to outcomes that are worse than sequential choice and discuss the circumstances when this is likely to be true.,
Organizational Behavior and Human Decision Processes
Erasmus School of Economics

Read, D., Antonides, G., van den Ouden, L., & Trienekens, H. (2001). Which Is Better: Simultaneous or Sequential Choice?. Organizational Behavior and Human Decision Processes, 84(1), 54–70. doi:10.1006/obhd.2000.2917