A behavioral approach of decision making under risk and uncertainty.

Summary This thesis focuses on how individuals make decisions in the presence of risk and uncertainty. It consists of four essays that theoretically and experimentally study decision making.The first two essays study situations where a decision maker must decide whether an event has occurred using uncertain information. Correctly identifying that this event has occurred is more rewarding than correctly identifying that it has not occurred. This decision problem induces a divergence between two qualities of a decision: optimality and accuracy. The two trials reproduce such situations in a perceptual task-based laboratory experiment and analyze the decisions using signal detection theory to study the optimality-accuracy trade-off. The first trial confirms the existence of such a trade-off with a dominant role of accuracy seeking. It explains the existence of this trade-off by non-monetary utility associated with being right. The second chapter shows that presenting perceptual information last contributes to the existence of the optimality-accuracy trade-off.The third essay studies how life-to-life preferences of others interact with the attitude toward ambiguity. It presents the results of an experiment in which subjects are asked to make donations to charities. Donations can have ambiguous costs or benefits. We find that ambiguity has the effect of making individuals more selfish. In other words, we show that individuals use ambiguity as an excuse not to give. This self-justifying behavior is stronger for ambiguous costs than for ambiguous benefits.The fourth test examines the external validity of risk preference measures in the laboratory using decisions in other risky experimental tasks and decisions made on outside the laboratory. We find that risk preference measures are able to explain the former, but do not explain the latter.