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This thesis focuses on the concept of loss aversion in cumulative prospect theory and applies cumulative prospect theory to explain people's consumption behavior and the issuance of stock options to both employees and executives. Firstly, I provide a canonical way to frame loss aversion in cumulative prospect theory. I formally define an index of loss aversion as a function to reflect gain/loss comparisons. This index, different from the one defined by Kobberling and Wakker (2005), can be naturally 'used to fully describe the characteristics of loss aversion. With this index, equivalent conditions for loss aversion and strong loss aversion can be achieved. Distinctions of my definition from the previous ones are discussed in details. I also attempt to fit the special classes of utility functions into my definition. Compar- ative loss aversion can be defined through Yaari's acceptance sets and a standard asset ./ allocation problem. The conclusion is: the more loss averse an agent is, the smaller the acceptance set is and the less she will invest in risky assets. Secondly, I create a cumulative prospect theory multiperiod model to explain the fact that employees like to be paid with stock options. Essentially, it is the psycho- logical characteristic that people are prone to overweight the probability for extreme large returns to make the stock option preferred to the Black-Scholes price or the cost to the company, even when there is no optimism among employees. Employees'desire to hold options increases as firm volatility or optimism increases. My model is also consistent with other observed facts such as typical exercise behavior. Loss aversion in cumulative prospect theory can trigger early exercise behavior when the stock price is high, since the fear for a future drop of the stock price dominates the potential hap- piness brought by future gains. I also analyse the executive's compensation package. I find that a multiperiod risk averse model will predict a high base salary and some positive holdings in stock options in the optimal package as observed in the empirical research. Finally, I try to solve the puzzle about people's asymmetric reaction to the ex- pected income changes. I extend Kimball's two-period consumption model through incorporating the psychological utility function from prospect theory. Still within the expected utility framework, the asymmetric effect of loss aversion and the definition of reference level increase the flexibility of the model. Now the optimal consumption is determined by risk aversion and prudence in the general consumption utility, loss aversion, risk aversion and prudence on gains, and risk loving and anti-prudence on losses in the psychological utility. The most important findings are: for 'habit stickers', when they expect the future income to increase, they increase their current consump- tion synchronously, but when they expect a decrease for their future income, they may not lower their current living standards; for those with fully-adjusted reference levels, when they hear good news about the future income, they do not substantially increase today's consumption, and they are prone to lower their current living standards in front of bad news.

La recherche portant sur l’évaluation monétaire de l’environnement est en pleine essor, en particulier dans le domaine de la biodiversité dont la dégradation apparaît comme l’un des enjeux environnementaux iconiques aujourd’hui. Il est souvent fait recourt à la théorie néoclassique de la valeur économique et de l’évaluation monétaire pour estimer la valeur de la biodiversité, et ce malgré la profusion d’analyses critiques de la théorie en elle-même, mais aussi de son applicabilité à l’objet biodiversité. Cette thèse de doctorat tente d’identifier les principaux facteurs de pertinence des évaluations monétaires pour les décideurs publics. Cette pertinence dépendant de façon schématique du contenu des évaluations et de leur légitimité. Nous analysons comme premier facteur le pouvoir d’influence de l’unité monétaire et de l’Analyse Coûts Bénéfices, comme second facteur l’altération possible dans l’approche éthique de l’économie qu’implique le recours à l’évaluation monétaire (rendant probablement l’analyse fortement anthropocentrique et purement instrumentale), comme troisième facteur les choix méthodologiques liés à l’actualisation, et comme dernier facteur la complexité de la notion biodiversité et en particulier à la complexité de sa dimension fonctionnelle. Traiter de ces facteurs conduit à utiliser et justifier une littérature et recherche interdisciplinaires portant sur la biodiversité, et un effort constant de la part des économistes de clarifier la nature de leur approche à l’objet d’étude biodiversité lorsqu’ils la valorisent monétairement. / There is a profusion of research on environmental monetary valuation methods, and particularly in ‘biodiversity valuations’ because biodiversity losses have become one of today’s two environmental iconic problems. Often, it is the neoclassical/welfare theory of the economic value and environmental asset valuation that is applied to value biodiversity. However, this theory raises many concerns, by itself, but also regarding its applicability to biodiversity. This PhD attempts to identify some major factors playing a role in the relevance of valuations for public decision makers, a relevance that schematically results from the content and the legitimacy of valuations. The first factor we deal with is the influential power of money and the Cost Benefit Analysis, the second is the shift in ethical approach that monetary valuations risk to bring to the general economic approach (strongly anthropocentric and merely instrumental), the third factor is the methodological recourse to discounting and the fourth factor is the complexity of the notion biodiversity and particularly of its functional dimension. To work on those factors, we emphasize the relevance and necessity, of an interdisciplinary research, and of a constant effort on the part of economists, to clarify the nature of their fundamental approach to biodiversity when having recourse to monetary valuations.