Deviations from rational beliefs: An investigation combining psychological and experimental economics approaches

Leslie Van Der Leer

Research output: ThesisDoctoral Thesis

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This thesis investigates various deviations from rational beliefs by combining methods from psychology and experimental economics.

The first two studies focused on the jumping-to-conclusions bias, where delusional and delusion-prone individuals tend to make decisions based on less data than controls. In an incentivised and adapted “beads task” probability-reasoning paradigm, the effects of delusion-proneness on decisions and on probability ratings were investigated. All participants, but especially more delusion-prone participants, made their decisions too early. Moreover, high delusion-prone participants’ probability ratings were less affected by incentives than low delusion-prone participants’.

The same paradigm was used to explore an inaccurate, but potentially evolutionarily advantageous, belief: the sexual over-perception bias, where men perceive more sexual interest in women’s behaviour than women report or perceive. No evidence was found for men’s over-perception of a male character’s appeal to women in a belief-updating paradigm, which may reflect conceptual and methodological limitations of previous work on this topic.

Perhaps, people deviate from rationality for certain purposes (e.g., evolutionary goals), while also holding an accurate, rational belief. The fourth study examined whether people are, at some level, aware that their optimistic beliefs are inaccurate, by combining two distinct belief-updating paradigms. Participants provided repeated answers to neutral questions and questions about undesirable future outcomes. Participants were equally accurate for neutral items, but were even more optimistic on the second guess for undesirable items, suggesting that optimism involves “real” self-deception.

The last study investigated another phenomenon where people may want to avoid undesirable information. Investors are less willing to invest when playing the trust game with another player than when playing a computerised lottery with the same odds of the outcomes, which suggests that observing potential betrayal carries an additional, emotional cost. It was found that beliefs about others’ trustworthiness could predict the level of such betrayal aversion.
Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • McKay, Ryan, Supervisor
Award date1 Apr 2015
Publication statusUnpublished - 2015


  • Psychology
  • Experimental Economics
  • jumping to conclusions
  • beads task
  • irrationality
  • self-deception
  • optimism bias
  • error management theory
  • trust game
  • betrayal aversion
  • sexual overperception

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