DISAMBIGUATING AMBIGUITY AVERSION: THE IMPACT OF EXPERIENCE, COMPARATIVE KNOWLEDGE AND COMPETITIVENESS ON DECISIONS IN THE ELLSBERG TASK

摘要

People strictly prefer events with known probabilities to those involving unknown probabilities, even under situations in which normative theories of decision-making predict indifference. This highly robust phenomenon is known as ambiguity aversion. The present thesis investigates three prominent factors underlying ambiguity aversion in Ellsberg-type betting tasks. Chapter 1 focuses on the effect of unknown probability distributions on the attitudes towards ambiguity. Different probability distributions, each providing subtly different information about the underlying properties of the ambiguous bet were either experienced through sampling or simply described to participants prior to choice. Overall, the results showed that people demonstrated ambiguity-neutral attitudes when the underlying probability distributions were experienced. In contrast, when described, ambiguity attitudes were contingent on the distribution type. Chapter 2 investigates whether (e)valuation of risky and ambiguous bets in the Ellsberg task would change when the decision maker's knowledge contrast between these two bets is weakened with the introduction of several other bets with different levels of informativeness. Findings demonstrated that the amount participants are willing to pay/accept for the risky and ambiguous bets changes in the presence of additional bets. Further this effect was shown to be driven primarily by devaluation of the risky bet. Chapter 3 investigates the impact of the relative state of knowledge and the perceived competitiveness of other individuals on the decision maker's degree of ambiguity aversion in hypothetical and real Ellsberg tasks. The results demonstrated that the level of ambiguity aversion changed primarily as a function of the perceived competitiveness of others, and that the effect of the relative state of knowledge was contingent on the level of perceived competitiveness. The obtained patterns were shown to be much stronger when people interacted with real competitors for real material benefits. The overall findings in the thesis help explain under which specific circumstances weak and strong forms of ambiguity aversion occurs.