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- Evaluating credit risk models: a critique and a new proposal (2001)
- Evaluating the quality of credit portfolio risk models is an important question for both banks and regulators. Lopez and Saidenberg (2000) suggest cross-sectional resampling techniques in order to make efficient use of available data and to produce measures of forecast accuracy. We first show that their proposal disregards crosssectional dependence in simulated subportfolios, which renders standard statistical inference invalid. We proceed by suggesting another evaluation methodology which draws on the concept of likelihood ratio tests. Specifically, we compare the predictive quality of alternative models by comparing the probabilities that observed data have been generated by these models. The distribution of the test statistic can be derived through Monte Carlo simulation. To exploit differences in cross-sectional predictions of alternative models, the test can be based on a linear combination of subportfolio statistics. In the construction of the test, the weight of a subportfolio depends on the difference in the loss distributions which alternative models predict for this particular portfolio. This makes efficient use of the data, and reduces computational burden. Monte Carlo simulations suggest that the power of the tests is satisfactory. JEL classification: G2; G28; C52

- Evaluating credit risk models : a critique and a proposal (2001)
- Evaluating the quality of credit portfolio risk models is an important issue for both banks and regulators. Lopez and Saidenberg (2000) suggest cross-sectional resampling techniques in order to make efficient use of available data. We show that their proposal disregards cross-sectional dependence in resampled portfolios, which renders standard statistical inference invalid. We proceed by suggesting the Berkowitz (1999) procedure, which relies on standard likelihood ratio tests performed on transformed default data. We simulate the power of this approach in various settings including one in which the test is extended to incorporate cross-sectional information. To compare the predictive ability of alternative models, we propose to use either Bonferroni bounds or the likelihood-ratio of the two models. Monte Carlo simulations show that a default history of ten years can be sufficient to resolve uncertainties currently present in credit risk modeling.

- SAFE Newsletter : 2014, Q3 (2014)

- Strategic complementarity, nominal rigidity and the non-neutrality of money : [Version September 1998] (1999)
- This paper examines whether an exogenous anticipated monetary shock causes real economic effects, i.e. whether anticipated money is neutral. A major finding is that an anticipated monetary shock can in fact be massively non-neutral in the shortrun, if the economic environment is characterized by strategic complementarity. If the environment is characterized by strategic substitutability, anticipated monetary shocks are largely neutral.

- Equity culture and the distribution of wealth (2013)
- Is wider access to stockholding opportunities related to reduced wealth inequality, given that it creates challenges for small and less sophisticated investors? Counterfactual analysis is used to study the influence of changes in the US stockholder pool and economic environment, on the distribution of stock and net household wealth during a period of dramatic increase in stock market participation. We uncover substantial shifts in stockholder pool composition, favoring smaller holdings during the 1990s upswing but larger holdings around the burst of the Internet bubble. We find no evidence that widening access to stocks was associated with reduced net wealth inequality.

- Systemic risk in the financial sector: what can we learn from option markets? : [version 10 february 2014] (2014)
- We propose a novel approach on how to estimate systemic risk and identify its key determinants. For US financial companies with publicly traded equity options, we extract option-implied value-at-risks and measure the spillover effects between individual company value-at-risks and the option-implied value-at-risk of a financial index. First, we study the spillover effect of increasing company risks on the financial sector. Second, we analyze which companies are mostly affected if the tail risk of the financial sector increases. Key metrics such as size, leverage, market-to-book ratio and earnings have a significant influence on the systemic risk profiles of financial institutions.

- The effects of a low interest rate environment on life insurers : [version july 2014] (2014)
- Low interest rates are becoming a threat to the stability of the life insurance industry, especially in countries such as Germany, where products with relatively high guaranteed returns sold in the past still represent a prominent share of the total portfolio. This contribution aims to assess and quantify the effects of the current low interest rate phase on the balance sheet of a representative German life insurer, given the current asset allocation and the outstanding liabilities. To do so, we generate a stochastic term structure of interest rates as well as stock market returns to simulate investment returns of a stylized life insurance business portfolio in a multi-period setting. Based on empirically calibrated parameters, we can observe the evolution of the life insurers' balance sheet over time with a special focus on their solvency situation. To account for different scenarios and in order to check the robustness of our findings, we calibrate different capital market settings and different initial situations of capital endowment. Our results suggest that a prolonged period of low interest rates would markedly affect the solvency situation of life insurers, leading to relatively high cumulative probability of default for less capitalized companies.

- A repeated principal-agent model with on-the-job search (2014)
- This paper analyzes how on-the-job search (OJS) by an agent impacts the moral hazard problem in a repeated principal-agent relationship. OJS is found to constitute a source of agency costs because efficient search incentives require that the agent receives all gains from trade. Further, the optimal incentive contract with OJS matches the design of empirically observed compensation contracts more accurately than models that ignore OJS. In particular, the optimal contract entails excessive performance pay plus efficiency wages. Efficiency wages reduce the opportunity costs of work effort and hence serve as a complement to bonuses. Thus, the model offers a novel explanation for the use of efficiency wages. When allowing for renegotiation, the model generates wage and turnover dynamics that are consistent with empirical evidence. I argue that the model contributes to explaining the concomitant rise in the use of performance pay and in competition for high-skill workers during the last three decades.

- Asset pricing and consumption-portfolio choice with recursive utility and unspanned risk : [version 4 august 2014] (2014)
- We study consumption-portfolio and asset pricing frameworks with recursive preferences and unspanned risk. We show that in both cases, portfolio choice and asset pricing, the value function of the investor/ representative agent can be characterized by a specific semilinear partial differential equation. To date, the solution to this equation has mostly been approximated by Campbell-Shiller techniques, without addressing general issues of existence and uniqueness. We develop a novel approach that rigorously constructs the solution by a fixed point argument. We prove that under regularity conditions a solution exists and establish a fast and accurate numerical method to solve consumption-portfolio and asset pricing problems with recursive preferences and unspanned risk. Our setting is not restricted to affine asset price dynamics. Numerical examples illustrate our approach.