An axiomatic characterization of capital allocations of coherent risk measures

An axiomatic definition of coherent capital allocations is given. It is shown that coherent capital allocations defined by the proposed axiom system are closely linked to coherent risk measures. More precisely, the associated risk measure of a coherent capital allocation is coherent and, conversely, for every coherent risk measure there exists a coherent capital allocation.     

Optimal human capital policies

We analyze optimal income taxes and optimal schooling subsidies in a dynamic private information economy with observable human capital accumulation. We show that under plausible conditions the marginal schooling subsidies are positive and that they are zero at both endpoints of the skill distribution.We compute the optimal policies and evaluate their impact over the transition and at the steady state. We find that the optimal schooling policies are significantly smaller than the optimal marginal income taxes. If optimal schooling policies are introduced jointly with optimal income taxes then their welfare and aggregate effects are small. However, if income taxes are not set optimally then the optimal schooling policies have significant welfare and aggregate effects.     

Optimal capital growth with convex shortfall penalties

The optimal capital growth strategy or Kelly strategy has many desirable properties such as maximizing the asymptotic long-run growth of capital. However, it has considerable short-run risk since the utility is logarithmic, with essentially zero Arrow–Pratt risk aversion. It is common to control risk with a Value-at-Risk (VaR) constraint defined on the end of horizon wealth. A more effective approach is to impose a VaR constraint at each time on the wealth path. In this paper, we provide a method to obtain the maximum growth while staying above an ex-ante discrete time wealth path with high probability, where shortfalls below the path are penalized with a convex function of the shortfall. The effect of the path VaR condition and shortfall penalties is a lower growth rate than the Kelly strategy, but the downside risk is under control. The asset price dynamics are defined by a model with Markov transitions between several market regimes and geometric Brownian motion for prices within a regime. The stochastic investment model is reformulated as a deterministic programme which allows the calculation of the optimal constrained growth wagers at discrete points in time.     

Update rules for convex risk measures

In the first part of the paper we investigate the properties that describe the intertemporal structure of dynamic convex risk measures. The usual backward approach to dynamic risk assessment leads to strong and weak versions of time consistency. As an alternative, we introduce a forward approach of consecutivity. In the second part we discuss the problem of how to update a convex risk measure when new information arrives. We analyse to what extent the above properties are appropriate update criteria.     

Optimal capital structure and endogenous default

In a sequence of fascinating papers, Leland and Leland and Toft have investigated various properties of the debt and credit of a firm which keeps a constant profile of debt and chooses its bankruptcy level endogenously, to maximise the value of the equity. One feature of these papers is that the credit spreads tend to zero as the maturity tends to zero, and this is not a feature which is observed in practice. This defect of the modelling is related to the diffusion assumptions made in the papers referred to; in this paper, we take a model for the value of the firm's assets which allows for jumps, and find that the spreads do not go to zero as maturity goes to zero. The modelling is quite delicate, but it just works; analysis takes us a long way, and for the final steps we have to resort to numerical methods.     

General convex order on risk aggregation

Using a general notion of convex order, we derive general lower bounds for risk measures of aggregated positions under dependence uncertainty, and this in arbitrary dimensions and for heterogeneous models. We also prove sharpness of the bounds obtained when each marginal distribution has a decreasing density. The main result answers a long-standing open question and yields an insight in optimal dependence structures. A numerical algorithm provides bounds for quantities of interest in risk management. Furthermore, our numerical results suggest that the bounds obtained in this paper are generally sharp for a broader class of models.     

发挥资本导向整合银行风险管理体制

近年来,资本管理在商业银行中的地位越来越重要,这是监管部门强调资本约束原则的效果,也是商业银行自身控制风险的重要手段。文章指出,作为商业银行风险管理工作的重要抓手,资本管理的核心是计量能力的提升,对于资本分配应掌握总量控制的原则。中国银行业应以资本管理为导向,逐步完善自身的风险管理体系。     

Optimal investments for risk- and ambiguity-averse preferences: a duality approach

Ambiguity, also called Knightian or model uncertainty, is a key feature in financial modeling. A recent paper by Maccheroni et al. (preprint, 2004) characterizes investor preferences under aversion against both risk and ambiguity. Their result shows that these preferences can be numerically represented in terms of convex risk measures. In this paper we study the corresponding problem of optimal investment over a given time horizon, using a duality approach and building upon the results by Kramkov and Schachermayer (Ann. Appl. Probab. 9, 904–950, 1999; Ann. Appl. Probab. 13, 1504–1516, 2003). Supported by Deutsche Forschungsgemeinschaft through the SFB 649 “Economic Risk”.     

Investment timing and optimal capital structure under liquidity risk

Deterioration in debt market liquidity reduces debt values and affects firms' decisions. Considering such risk, we develop an investment timing model and obtain analytic solutions. We carry out a comprehensive analysis in optimal financing, default, and investment strategies, and stockholder–bondholder conflicts. Our model explains stylized facts and replicates empirical findings in credit spreads. We obtain six new insights for decision makers. We propose a ‘new trade-off theory’ for optimal capital structure, a new tax effect, and new explanations of ‘debt conservatism puzzle’ and ‘zero-leverage puzzle’. Failure in recognizing liquidity risk results in substantially over-leveraging, early bankruptcy or investment, overpriced options, and undervalued coupons and credit spreads. In addition, agency costs are surprisingly small for a high liquidity risk or a low project risk. Interestingly, the risk shifting incentive and debt overhang problem decrease with liquidity risk under moderate tax rates while they increase under high tax rates.     

Information dissemination on intellectual capital in mergers and acquisitions: purchase price allocations,press releases and business press

In order to reduce information asymmetries in relation to a firm's current decisions and long-term strategy, firms must consistently provide information to stakeholders. This paper investigates intellectual capital (IC) information disclosed in mergers and acquisitions (M&A) provided through three different disclosure channels (voluntary press releases, related newspaper articles and subsequent mandatory corporate disclosures in the notes to the financial statements). For a sample of 215 randomly selected US and European M&As, we analyse 215 press releases, 1025 newspaper articles and 215 purchase price allocations. Our findings suggest that IC disclosure in press releases is not perceived as informative and qualitative forward-looking IC information in voluntary corporate disclosures appears to lack credibility. Moreover, we empirically demonstrate interdependencies across the three disclosure channels. The business press seems to filter IC information provided in press releases. The amount of IC disclosure in the notes to the financial statements is positively associated with prior IC disclosure in newspaper articles, but negatively associated with IC disclosure in press releases. The managements of acquirer firms appear to pay attention to news coverage and public opinion. However, both voluntary and mandatory corporate disclosures appear to substitute rather than complement each other.     

Optimal mean-reversion strategy in the presence of bid-ask spread and delays in capital allocations

A portfolio optimization problem for an investor who trades T-bills and a mean-reverting stock in the presence of proportional and convex transaction costs is considered. The proportional transaction cost represents a bid-ask spread, while the convex transaction cost is used to model delays in capital allocations. I utilize the historical bid-ask spread in US stock market and assume that the stock reverts on yearly basis, while an investor follows monthly changes in the stock price. It is found that proportional transaction cost has a relatively weak effect on the expected return and the Sharpe ratio of the investor's portfolio. Meantime, the presence of delays in capital allocations has a dramatic impact on the expected return and the Sharpe ratio of the investor's portfolio. I also find the robust optimal strategy in the presence of model uncertainty and show that the latter increases the effective risk aversion of the investor and makes her view the stock as more risky.     

Optimal reinsurance under general law-invariant risk measures

In recent years, general risk measures play an important role in risk management in both finance and insurance industry. As a consequence, there is an increasing number of research on optimal reinsurance decision problems using risk measures beyond the classical expected utility framework. In this paper, we first show that the stop-loss reinsurance is an optimal contract under law-invariant convex risk measures via a new simple geometric argument. A similar approach is then used to tackle the same optimal reinsurance problem under Value at Risk and Conditional Tail Expectation; it is interesting to note that, instead of stop-loss reinsurances, insurance layers serve as the optimal solution. These two results highlight that law-invariant convex risk measure is better and more robust, in the sense that the corresponding optimal reinsurance still provides the protection coverage against extreme loss irrespective to the potential increment of its probability of occurrence, to expected larger claim than Value at Risk and Conditional Tail Expectation which are more commonly used. Several illustrative examples will be provided.     

The two faces of social capital in private flood mitigation: opposing effects on risk perception,self-efficacy and coping capacity

Impacts of flooding are expected to increase, most notably in residential areas. As a consequence, private households are increasingly encouraged to engage in private flood mitigation complementary to public measures. Despite the growing literature on private flood mitigation, little is known about how social capital influences households’ perception of and coping with flood risks. This study draws on survey data of 226 flood-prone households in two Austrian Alpine municipalities, both recently affected by riverine flooding. We show that social capital cuts both ways: on the positive side, social capital increases perceived self-efficacy and provides critical support during and most notably after flood events. On the negative side, social capital reduces flood risk perceptions of private households. While social ties are effective when responding to and recovering from floods, the expectation of social support downplays risk, making precautionary action by households less likely. The results also show that flood-affected households receive more social support than they provide to others. In the long-run, this can lead to a problematic reciprocity imbalance, challenging the long-term stability of the interpersonal exchanges underlying social capital. Among the various sources of social support, informal social networks (neighbours, friends and relatives) provide the most important workforce in the response and recovery phase of a flood event. It is therefore crucial for flood risk management to recognise and promote the protective quality of social capital alongside conventional structural and non-structural measures.     

Optimal execution strategies in limit order books with general shape functions

We consider optimal execution strategies for block market orders placed in a limit order book (LOB). We build on the resilience model proposed by Obizhaeva and Wang (2005 Obizhaeva, A and Wang, J. 2005. Optimal trading strategy and supply/demand dynamics, Preprint Available online at: http://www.rhsmith.umd.edu/faculty/obizhaeva/OW060408.pdf (accessed 16 February 2009)[Crossref] , [Google Scholar]) but allow for a general shape of the LOB defined via a given density function. Thus, we can allow for empirically observed LOB shapes and obtain a nonlinear price impact of market orders. We distinguish two possibilities for modelling the resilience of the LOB after a large market order: the exponential recovery of the number of limit orders, i.e. of the volume of the LOB, or the exponential recovery of the bid–ask spread. We consider both of these resilience modes and, in each case, derive explicit optimal execution strategies in discrete time. Applying our results to a block-shaped LOB, we obtain a new closed-form representation for the optimal strategy of a risk-neutral investor, which explicitly solves the recursive scheme given in Obizhaeva and Wang (2005 Obizhaeva, A and Wang, J. 2005. Optimal trading strategy and supply/demand dynamics, Preprint Available online at: http://www.rhsmith.umd.edu/faculty/obizhaeva/OW060408.pdf (accessed 16 February 2009)[Crossref] , [Google Scholar]). We also provide some evidence for the robustness of optimal strategies with respect to the choice of the shape function and the resilience-type.