The estimation of probabilities of default (PDs) for low default portfolios
by means of upper confidence bounds is a well established procedure in many
financial institutions. However, there are often discussions within the
institutions or between institutions and supervisors about which confidence
level to use for the estimation. The Bayesian estimator for the PD based on the
uninformed, uniform prior distribution is an obvious alternative that avoids
the choice of a confidence level.
The important application of semi-static hedging in financial markets
naturally leads to the notion of quasi self-dual processes. The focus of our
study is to give new characterizations of quasi self-duality for exponential
L\'evy processes such that the resulting market does not admit arbitrage
opportunities. We derive a set of equivalent conditions for the stochastic
logarithm of quasi self-dual martingale models and derive a further
characterization of these models not depending on the L\'evy-Khintchine
parametrization.
We propose a generalization of the classical notion of the $V@R_{\lambda}$
that takes into account not only the probability of the losses, but the balance
between such probability and the amount of the loss. This is obtained by
defining a new class of law invariant risk measures based on an appropriate
family of acceptance sets. The $V@R_{\lambda}$ and other known law invariant
risk measures turn out to be special cases of our proposal.
We provide a dual representation of quasiconvex conditional risk measures $%
\rho $ defined on $L^{0}$ modules of the $L^{p}$ type. This is a consequence of
more general result which extend the usual Penot-Volle representation for
quasiconvex real valued maps. We establish, in the conditional setting, a
complete duality between quasiconvex risk measures and the appropriate class of
dual functions.
The paper concerns primal and dual representations as well as time
consistency of set-valued dynamic risk measures. Set-valued risk measures
appear naturally when markets with transaction costs are considered and capital
requirements can be made in a basket of currencies or assets. Time consistency
of scalar risk measures can be generalized to set-valued risk measures in
different ways.
The adverse effects of financial crises in terms of output losses or output
growth below its potential can be treated like losses from catastrophic events
which have a low likelihood but a large impact in the event that they occur.
There is empirical evidence that recovery rates tend to go down just when the
number of defaults goes up in economic downturns. This has to be taken into
account in estimation of the capital against credit risk required by Basel II
to cover losses during the adverse economic downturns; the so-called "downturn
LGD" requirement. This paper presents estimation of the LGD credit risk model
with default and recovery dependent via the latent systematic risk factor using
Bayesian inference approach and Markov chain Monte Carlo method.
Propagation of balance-sheet or cash-flow insolvency across financial
institutions may be modeled as a cascade process on a network representing
their mutual exposures. We derive rigorous asymptotic results for the magnitude
of contagion in a large financial network and give an analytical expression for
the asymptotic fraction of defaults, in terms of network characteristics. Our
results extend previous studies on contagion in random graphs to inhomogeneous
directed graphs with a given degree sequence and arbitrary distribution of
weights.
We present a computational method for measuring financial risk by estimating
the Value at Risk and Expected Shortfall from financial series. We have made
two assumptions: First, that the predictive distributions of the values of an
asset are conditioned by information on the way in which the variable evolves
from similar conditions, and secondly, that the underlying random processes can
be described using piecewise Gaussian processes.
The global financial system has become highly connected and complex. Has been
proven in practice that existing models, measures and reports of financial risk
fail to capture some important systemic dimensions. Only lately, advisory
boards have been established in high level and regulations are directly
targeted to systemic risk. In the same direction, a growing number of
researchers employ network analysis to model systemic risk in financial
networks. Current approaches are concentrated on interbank payment network
flows in national and international level.
Unlike other industries in which intellectual property is patentable, the
financial industry relies on trade secrecy to protect its business processes
and methods, which can obscure critical financial risk exposures from
regulators and the public. We develop methods for sharing and aggregating such
risk exposures that protect the privacy of all parties involved and without the
need for a trusted third party.
In this paper we look at the efficacy of different risk measures on energy
markets and across several different stock market indices. We use both the
Value at Risk and the Tail Conditional Expectation on each of these data sets.
We also consider several different durations and levels for historical risk
measures. Through our results we make some recommendations for a robust risk
management strategy that involves historical risk measures.
Regulation and risk management in banks depend on underlying risk measures.
In general this is the only purpose that is seen for risk measures. In this
paper we suggest that the reporting of risk measures can be used to determine
the loss distribution function for a financial entity. We demonstrate that a
lack of sufficient information can lead to ambiguous risk situations. We give
examples, showing the need for the reporting of multiple risk measures in order
to determine a bank's loss distribution.
The banking systems that deal with risk management depend on underlying risk
measures. Following the Basel II accord, there are two separate methods by
which banks may determine their capital requirement. The Value at Risk measure
plays an important role in computing the capital for both approaches. In this
paper we analyze the errors produced by using this measure. We discuss other
measures, demonstrating their strengths and shortcomings. We give examples,
showing the need for the information from multiple risk measures in order to
determine a bank's loss distribution.
The inverse first passage time problem asks whether, for a Brownian motion
$B$ and a nonnegative random variable $\zeta$, there exists a time-varying
barrier $b$ such that $\mathbb{P}\{B_s > b(s), \, 0 \le s \le t\} =
\mathbb{P}\{\zeta > t\}$. We study a "smoothed" version of this problem and ask
whether there is a "barrier" $b$ such that $\mathbb{E}[\exp(-\lambda \int_0^t
\psi(B_s - b(s)) \, ds)] = \mathbb{P}\{\zeta > t\}$, where $\lambda$ is a
killing rate parameter and $\psi: \mathbb{R} \to [0,1]$ is a non-increasing
function.
In this paper, we introduce a multivariate extension of the classical
univariate Value- at-Risk (VaR). This extension may be useful to understand how
solvency capital re- quirement computed for a given financial institution may
be affected by the presence of additional risks. We also generalize the
bivariate Conditional-Tail-Expectation (CTE), previously introduced by Di
Bernardino et al. (2011), in a multivariate set- ting and we study its
behavior. Several properties have been derived.
The benefits of diversifying risks are difficult to estimate quantitatively
because of the uncertainties in the dependence structure between the risks.
Also, the modelling of multidimensional dependencies is a non-trivial task.
This paper focuses on one such technique for portfolio aggregation, namely the
aggregation of risks within trees, where dependencies are set at each step of
the aggregation with the help of some copulas.
Threats on the stability of a financial system may severely affect the
functioning of the entire economy, and thus considerable emphasis is placed on
the analyzing the cause and effect of such threats. The financial crisis in the
current and past decade has shown that one important cause of instability in
global markets is the so-called financial contagion, namely the spreading of
instabilities or failures of individual components of the network to other,
perhaps healthier, components.
Karl Menger's 1934 paper on the St. Petersburg paradox contains mathematical
errors that invalidate his conclusion that unbounded utility functions,
specifically Bernoulli's logarithmic utility, fail to resolve modified versions
of the St. Petersburg paradox.
Starting from the requirement that risk measures of financial portfolios
should be based on their losses, not their gains, we define the notion of
loss-based risk measure and study the properties of this class of risk
measures. We characterize loss-based risk measures by a representation theorem
and give examples of such risk measures.
The problem of stock hedging is reconsidered in this paper, where a put
option is chosen from a set of available put options to hedge the market risk
of a stock. A formula is proposed to determine the probability that the
potential loss exceeds a predetermined level of Value-at-Risk, which is used to
find the optimal strike price and optimal hedge ratio. The assumptions that the
chosen put option finishes in-the-money and the constraint of hedging budget is
binding are relaxed in this paper.
This paper derives explicit formulas for both the small and large time limits
of the implied volatility in the minimal market model. It is shown that
interest rates do impact on the implied volatility in the long run even though
they are negligible in the short time limit.
In this paper we estimate the propagation of liquidity shocks through
interbank markets when the information about the underlying credit network is
incomplete. We show that techniques such as Maximum Entropy currently used to
reconstruct credit networks severely underestimate the risk of contagion by
assuming a trivial (fully connected) topology, a type of network structure
which can be very different from the one empirically observed.
This article makes use of the apparent indifference that the market has been
devoting to the developments made on the fundamentals of quantitative finance,
to introduce novel insight for better understanding market evolution.We show
how these drops and crises emerge as a natural result of local economical
principles ruling trades between economical agents and present evidence that
heavy-tails of the return distributions are bounded by constraints associated
with the topology of agent relations. Finally, we discuss how these constraints
may be helpful for properly evaluate model risk.
We prove a law of large numbers for the loss from default and use it for
approximating the distribution of the loss from default in large, potentially
heterogenous portfolios. The density of the limiting measure is shown to solve
a non-linear SPDE, and the moments of the limiting measure are shown to satisfy
an infinite system of SDEs. The solution to this system leads to %the solution
to the SPDE through an inverse moment problem, and to the distribution of the
limiting portfolio loss, which we propose as an approximation to the loss
distribution for a large portfolio.
In this work, we consider the hedging error due to discrete trading in models
with jumps. Extending an approach developped by Fukasawa (2011) for continuous
processes, we propose a framework enabling to (asymptotically) optimize the
discretization times. More precisely, a discretization rule is said to be
optimal if for a given cost function, no strategy has (asymptotically, for
large cost) a lower mean square discretization error for a smaller cost. We
focus on discretization rules based on hitting times and give explicit
expressions for the optimal rules within this class.
Financial volatility risk is addressed through a multiple round evolutionary
quantum game equilibrium leading to Multifractal Self-Organized Criticality
(MSOC) in the financial returns and in the risk dynamics. The model is
simulated and the results are compared with financial volatility data.
A simple, yet reasonably accurate, analytical technique is proposed for
multi-factor structural credit portfolio models. The accuracy of the technique
is demonstrated by benchmarking against Monte Carlo simulations. The approach
presented here may be of high interest to practitioners looking for
transparent, intuitive, easy to implement and high performance credit portfolio
model.
A risk of small defined-benefit pension schemes is that there are too few
members to eliminate idiosyncratic mortality risk, that is there are too few
members to effectively pool mortality risk. This means that when there are few
members in the scheme, there is an increased risk of the liability value
deviating significantly from the expected liability value, as compared to a
large scheme.
In this paper, we detail the main simulation methods used in practice to
measure one-year reserve risk, and describe the bootstrap method providing an
empirical distribution of the Claims Development Result (CDR) whose variance is
identical to the closed-form expression of the prediction error proposed by
W\"uthrich et al. (2008). In particular, we integrate the stochastic modeling
of a tail factor in the bootstrap procedure. We demonstrate the equivalence
with existing analytical results and develop closed-form expressions for the
error of prediction including a tail factor.
In this paper, we investigate two different frameworks for assessing the risk
in a multi-period decision process: a dynamically inconsistent formulation
(whereby a single, static risk measure is applied to the entire sequence of
future costs), and a dynamically consistent one, obtained by suitably composing
one-step risk mappings. We characterize the class of dynamically consistent
measures that provide a tight approximation for a given inconsistent measure,
and discuss how the approximation factors can be computed.
This research presents an analysis of the demographic risk related to future
membership patterns in pension funds with restricted entrance, financed under a
pay-as-you-go scheme. The paper, therefore, proposes a stochastic model for
investigating the behaviour of the demographic variable "new entrants" and the
influence it exerts on the financial dynamics of such funds. Further
information on pension funds of Italian professional categories and an
application to the Cassa Nazionale di Previdenza e Assistenza dei Dottori
Commercialisti (CNPADC) are then provided.
Recent academic work has developed a method to determine, in real time, if a
given stock is exhibiting a price bubble. Currently there is speculation in the
financial press concerning the existence of a price bubble in the aftermath of
the recent IPO of LinkedIn. We analyze stock price tick data from the short
lifetime of this stock through May 24, 2011, and we find that LinkedIn has a
price bubble.
This paper presents two cases of random banking data generators based on
migration matrices and scoring rules. The banking data generator is a new hope
in researches of finding the proving method of comparisons of various credit
scoring techniques. There is analyzed the influence of one cyclic
macro--economic variable on stability in the time account and client
characteristics. Data are very useful for various analyses to understand in the
better way the complexity of the banking processes and also for students and
their researches.
The classical reduced-form and filtration expansion framework in credit risk
is extended to the case of multiple, non-ordered defaults, assuming that
conditional densities of the default times exist. Intensities and pricing
formulas are derived, revealing how information driven default contagion arises
in these models. We then analyze the impact of ordering the default times
before expanding the filtration.
We analyze the counterparty risk embedded in CDS contracts, in presence of a
bilateral margin agreement. First, we investigate the pricing of collateralized
counterparty risk and we derive the bilateral Credit Valuation Adjustment
(CVA), unilateral Credit Valuation Adjustment (UCVA) and Debt Valuation
Adjustment (DVA). We propose a model for the collateral by incorporating all
related factors such as the thresholds, haircuts and margin period of risk. We
derive the dynamics of the bilateral CVA in a general form with related jump
martingales.
We develop a dynamic point process model of correlated default timing in a
portfolio of firms, and analyze typical and atypical default profiles in the
limit as the size of the pool grows. In our model, a name defaults at a
stochastic intensity that is influenced by an idiosyncratic risk process, a
systematic risk process common to all names, and past defaults. We prove a law
of large numbers for the default rate in the pool, which describes the
"typical" behavior of defaults.
The problem behind this paper is the proper measurement of the degree of
quality/acceptability/distance to arbitrage of trades. We are narrowing the
class of coherent acceptability indices introduced by Cherny and Madan (2007)
by imposing an additional mathematical property. For this, we introduce the
notion of a concave distortion semigroup as a family $(\Psi_t)_{t\ge0}$ of
concave increasing functions $[0,1]\to[0,1]$ satisfying the semigroup property
$$ \Psi_s\circ\Psi_t=\Psi_{s+t},\quad s,t\ge0.
We study an asymptotic behaviour of the difference between value-at-risks
VaR(L) and VaR(L+S) for heavy-tailed random variables L and S as an application
to sensitivity analysis of quantitative operational risk management in the
framework of an advanced measurement approach (AMA) of Basel II. We have
different types of results according to the magnitude relationship of thickness
of tails of L and S. Especially if the tail of S is enough thinner than the one
of L, then VaR(L + S) - VaR(L) is asymptotically equivalent to an expected loss
of S when L and S are independent.
Risk aversion is a key element of utility maximizing hedge strategies;
however, it has typically been assigned an arbitrary value in the literature.
This paper instead applies a GARCH-in-Mean (GARCH-M) model to estimate a
time-varying measure of risk aversion that is based on the observed risk
preferences of energy hedging market participants. The resulting estimates are
applied to derive explicit risk aversion based optimal hedge strategies for
both short and long hedgers.
A key issue in the estimation of energy hedges is the hedgers' attitude
towards risk which is encapsulated in the form of the hedgers' utility
function. However, the literature typically uses only one form of utility
function such as the quadratic when estimating hedges. This paper addresses
this issue by estimating and applying energy market based risk aversion to
commonly applied utility functions including log, exponential and quadratic,
and we incorporate these in our hedging frameworks.
This paper discusses the financial risks faced by the UK Pension Protection
Fund (PPF) and what, if anything, it can do about them. It draws lessons from
the regulatory regimes under which other financial institutions, such as banks
and insurance companies, operate and asks why pension funds are treated
differently. It also reviews the experience with other government-sponsored
insurance schemes, such as the US Pension Benefit Guaranty Corporation, upon
which the PPF is modelled.
This paper examines the volatility and covariance dynamics of cash and
futures contracts that underlie the Optimal Hedge Ratio (OHR) across different
hedging time horizons. We examine whether hedge ratios calculated over a short
term hedging horizon can be scaled and successfully applied to longer term
horizons. We also test the equivalence of scaled hedge ratios with those
calculated directly from lower frequency data and compare them in terms of
hedging effectiveness.
We present a novel procedure for scaling relatively high frequency tail
probability and quantile estimates for the conditional distribution of returns.
Risk is an inherent feature of agricultural production and marketing and
accurate measurement of it helps inform more efficient use of resources. This
paper examines three tail quantile-based risk measures applied to the
estimation of extreme agricultural financial risk for corn and soybean
production in the US: Value at Risk (VaR), Expected Shortfall (ES) and Spectral
Risk Measures (SRMs). We use Extreme Value Theory (EVT) to model the tail
returns and present results for these three different risk measures using
agricultural futures market data.
This paper presents non-parametric estimates of spectral risk measures
applied to long and short positions in 5 prominent equity futures contracts. It
also compares these to estimates of two popular alternative measures, the
Value-at-Risk (VaR) and Expected Shortfall (ES). The spectral risk measures are
conditioned on the coefficient of absolute risk aversion, and the latter two
are conditioned on the confidence level. Our findings indicate that all risk
measures increase dramatically and their estimators deteriorate in precision
when their respective conditioning parameter increases.
Spectral risk measures are attractive risk measures as they allow the user to
obtain risk measures that reflect their risk-aversion functions. To date there
has been very little guidance on the choice of risk-aversion functions
underlying spectral risk measures. This paper addresses this issue by examining
two popular risk aversion functions, based on exponential and power utility
functions respectively. We find that the former yields spectral risk measures
with nice intuitive properties, but the latter yields spectral risk measures
that can have perverse properties.
Spectral risk measures (SRMs) are risk measures that take account of user
riskaversion, but to date there has been little guidance on the choice of
utility function underlying them. This paper addresses this issue by examining
alternative approaches based on exponential and power utility functions. A
number of problems are identified with both types of spectral risk measure.
This paper examines the precision of estimators of Quantile-Based Risk
Measures (Value at Risk, Expected Shortfall, Spectral Risk Measures). It first
addresses the question of how to estimate the precision of these estimators,
and proposes a Monte Carlo method that is free of some of the limitations of
existing approaches. It then investigates the distribution of risk estimators,
and presents simulation results suggesting that the common practice of relying
on asymptotic normality results might be unreliable with the sample sizes
commonly available to them.
This letter uses the Block Maxima Extreme Value approach to quantify
catastrophic risk in international equity markets. Risk measures are generated
from a set threshold of the distribution of returns that avoids the pitfall of
using absolute returns for markets exhibiting diverging levels of risk. From an
application to leading markets, the letter finds that the Nikkei is more prone
to catastrophic risk than the FTSE and Dow Jones Indexes.
Value at risk (VaR) is a risk measure that has been widely implemented by
financial institutions. This paper measures the correlation among asset price
changes implied from VaR calculation. Empirical results using US and UK equity
indexes show that implied correlation is not constant but tends to be higher
for events in the left tails (crashes) than in the right tails (booms).
This paper applies the Extreme-Value (EV) Generalised Pareto distribution to
the extreme tails of the return distributions for the S&P500, FT100, DAX, Hang
Seng, and Nikkei225 futures contracts. It then uses tail estimators from these
contracts to estimate spectral risk measures, which are coherent risk measures
that reflect a user's risk-aversion function. It compares these to VaR and
Expected Shortfall (ES) risk measures, and compares the precision of their
estimators.
Accurate forecasting of risk is the key to successful risk management
techniques. Using the largest stock index futures from twelve European bourses,
this paper presents VaR measures based on their unconditional and conditional
distributions for single and multi-period settings. These measures underpinned
by extreme value theory are statistically robust explicitly allowing for
fat-tailed densities. Conditional tail estimates are obtained by adjusting the
unconditional extreme value procedure with GARCH filtered returns.
This paper empirically analyses risk in the Euro relative to other
currencies. Comparisons are made between a sub period encompassing the final
transitional stage to full monetary union with a sub period prior to this.
Stability in the face of speculative attack is examined using Extreme Value
Theory to obtain estimates of tail exchange rate changes. The findings are
encouraging. The Euro's common risk measures do not deviate substantially from
other currencies.
Key to the imposition of appropriate minimum capital requirements on a daily
basis requires accurate volatility estimation. Here, measures are presented
based on discrete estimation of aggregated high frequency UK futures
realisations underpinned by a continuous time framework. Squared and absolute
returns are incorporated into the measurement process so as to rely on the
quadratic variation of a diffusion process and be robust in the presence of fat
tails.
Both in practice and in the academic literature, models for setting margin
requirements in futures markets classically use daily closing price changes.
However, as well documented by research on high-frequency data, financial
markets have recently shown high intraday volatility, which could bring more
risk than expected. This paper tries to answer two questions relevant for
margin committees in practice: is it right to compute margin levels based on
closing prices and ignoring intraday dynamics? Is it justified to implement
intraday margin calls?
Spectral risk measures are attractive risk measures as they allow the user to
obtain risk measures that reflect their subjective risk-aversion. This paper
examines spectral risk measures based on an exponential utility function, and
finds that these risk measures have nice intuitive properties.
This paper applies an AR(1)-GARCH (1, 1) process to detail the conditional
distributions of the return distributions for the S&P500, FT100, DAX, Hang
Seng, and Nikkei225 futures contracts. It then uses the conditional
distribution for these contracts to estimate spectral risk measures, which are
coherent risk measures that reflect a user's risk-aversion function.
This paper investigates the hedging effectiveness of a dynamic moving window
OLS hedging model, formed using wavelet decomposed time-series. The wavelet
transform is applied to calculate the appropriate dynamic minimum-variance
hedge ratio for various hedging horizons for a number of assets.
The social role of any company is to get the maximum profitability with the
less risk. Due to Basel III, banks should now raise their minimum capital
levels on an individual basis, with the aim of lowering the probability for a
large crash to occur. Such implementation assumes that with higher minimum
capital levels it becomes more probable that the value of the assets drop
bellow the minimum level and consequently expects the number of bank defaults
to drop also.
In recent years research on credit risk modelling has mainly focused on
default probabilities. Recovery rates are usually modelled independently, quite
often they are even assumed constant. Then, however, the structural connection
between recovery rates and default probabilities is lost and the tails of the
loss distribution can be underestimated considerably. The problem of
underestimating tail losses becomes even more severe, when calibration issues
are taken into account. To demonstrate this we choose a Merton-type structural
model as our reference system.
We study the problem of portfolio insurance from the point of view of a fund
manager, who guarantees to the investor that the portfolio value at maturity
will be above a fixed threshold. If, at maturity, the portfolio value is below
the guaranteed level, a third party will refund the investor up to the
guarantee. In exchange for this protection, the third party imposes a limit on
the risk exposure of the fund manager, in the form of a convex monetary risk
measure.
We consider a structural model for the estimation of credit risk based on
Merton's original model. By using Random-Matrix theory we demonstrate
analytically that the presence of correlations severely limits the effect of
diversification in a credit portfolio if the correlation are not identical
zero. The existence of correlations alters the tails of the loss distribution
tremendously, even if their average is zero. Under the assumption of randomly
fluctuating correlations, a lower bound for the estimation of the loss
distribution is provided.
According to the Loss Distribution Approach, the operational risk of a bank
is determined as 99.9% quantile of the respective loss distribution, covering
unexpected severe events. The 99.9% quantile can be considered a tail event.
As part of Basel II's incremental risk charge (IRC) methodology, this paper
summarizes our extensive investigations of constructing transition probability
matrices (TPMs) for unsecuritized credit products in the trading book. The
objective is to create monthly or quarterly TPMs with predefined sectors and
ratings that are consistent with the bank's Basel PDs. Constructing a TPM is
not a unique process.
This paper introduces a new model risk measure based on hedging strategies to
estimate model risk and provision calculation under uncertainty of volatility.
This measure allows comparing different products and models (pricing
hypothesis) under a homogeneous framework and conclude which one is the best.
The model risk measure is defined in terms of the expected value and standard
deviation of the loss given by the hedging strategy at a given time horizon. It
has been assumed that the market volatility surface is driven by Heston's
dynamics calibrated to market for a given time horizon.
Under the Basel II standards, the Operational Risk (OpRisk) advanced
measurement approach is not prescriptive regarding the class of statistical
model utilised to undertake capital estimation. It has however become well
accepted to utlise a Loss Distributional Approach (LDA) paradigm to model the
individual OpRisk loss process corresponding to the Basel II Business
line/event type. In this paper we derive a novel class of doubly stochastic
alpha-stable family LDA models.
The current research on credit risk is primarily focused on modeling default
probabilities. Recovery rates are often treated as an afterthought; they are
modeled independently, in many cases they are even assumed constant. This is
despite of their pronounced effect on the tail of the loss distribution. Here,
we take a step back, historically, and start again from the Merton model, where
defaults and recoveries are both determined by an underlying process. Hence,
they are intrinsically connected.
In the present work we address the problem of evaluating the historical
performance of a trading strategy or a certain portfolio of assets. Common
indicators such as the Sharpe ratio and the risk adjusted return have
significant drawbacks. In particular, they are global indices, that is they do
not preserve any 'local' information about the performance dynamics either in
time or for a particular investment horizon. This information could be
fundamental for practitioners as the past performance can be affected by the
non-stationarity of financial market.
In order to protect brokers from customer defaults in a volatile market, an
active margin system is proposed for the transactions of margin lending in
China. The probability of negative return under the condition that collaterals
are liquidated in a falling market is used to measure the risk associated with
margin loans, and a recursive algorithm is proposed to calculate this
probability under a Markov chain model. The optimal maintenance margin ratio
can be given under the constraint of the proposed risk measurement for a
specified amount of initial margin.
This paper generalizes the framework for arbitrage-free valuation of
bilateral counterparty risk to the case where collateral is included, with
possible re-hypotecation. We analyze how the payout of claims is modified when
collateral margining is included in agreement with current ISDA documentation.
We then specialize our analysis to interest-rate swaps as underlying portfolio,
and allow for mutual dependences between the default times of the investor and
the counterparty and the underlying portfolio risk factors.
The downside risk of a portfolio of (equity)assets is generally substantially
higher than the downside risk of its components. In particular in times of
crises when assets tend to have high correlation, the understanding of this
di?erence can be crucial in managing systemic risk of a portfolio. In this
paper we gen- eralize Merton's option formula in the presence jumps to the
multi-asset case. It is shown how common jumps across assets provide an
intuitive and powerful tool to describe systemic risk that is consistent with
data.
This paper develops a structural credit risk model to characterize the
difference between the economic and recorded default times for a firm. Recorded
default occurs when default is recorded in the legal system. The economic
default time is the last time when the firm is able to pay off its debt prior
to the legal default time. It has been empirically documented that these two
times are distinct (see Guo, Jarrow, and Lin (2008)).
Set-valued risk measures on $L^p_d$ with $0 \leq p \leq \infty$ for conical
market models are defined, primal and dual representation results are given.
The collection of initial endowments which allow to super-hedge a multivariate
claim are shown to form the values of a set-valued sublinear (coherent) risk
measure. Scalar risk measures with multiple eligible assets also turn out to be
a special case within the set-valued framework.
It is well known that any sufficiently regular one-dimensional payoff
function has an explicit static hedge by bonds, forward contracts and lots of
vanilla options. We show that the natural extension of the corresponding
representation leads to a static hedge based on the same instruments along with
traffic light options, which have recently been introduced in the market. One
big advantage of these replication strategies is the easy structure of the
hedge. Hence, traffic light options are particularly powerful building blocks
for more complicated bivariate options.
This paper studies multidimensional dynamic risk measure induced by
conditional $g$-expectation. A notion of multidimensional $g$-expectation is
proposed to provide a multidimensional version of nonlinear expectations.
We consider dynamic sublinear expectations (i.e., time-consistent coherent
risk measures) whose scenario sets consist of singular measures corresponding
to a general form of volatility uncertainty. We derive a c\`adl\`ag nonlinear
martingale which is also the value process of a superhedging problem. The
superhedging strategy is obtained from a representation similar to the optional
decomposition. Furthermore, we prove an optional sampling theorem for the
nonlinear martingale and characterize it as the solution of a second order
backward SDE.
This paper investigates the impact of parameter uncertainty on capital
estimate in the well-known extended Loss Given Default (LGD) model with
systematic dependence between default and recovery. We demonstrate how the
uncertainty can be quantified using the full posterior distribution of model
parameters obtained from Bayesian inference via Markov chain Monte Carlo
(MCMC). Results show that the parameter uncertainty and its impact on capital
can be very significant.
We analyze the size dependence and temporal stability of firm bankruptcy risk
in the US economy by applying Zipf scaling techniques. We focus on a single
risk factor-the debt-to-asset ratio R-in order to study the stability of the
Zipf distribution of R over time. We find that the Zipf exponent increases
during market crashes, implying that firms go bankrupt with larger values of R.
Based on the Zipf analysis, we employ Bayes's theorem and relate the
conditional probability that a bankrupt firm has a ratio R with the conditional
probability of bankruptcy for a firm with a given R value.
We consider an insurance company in the case when the premium rate is a
bounded non-negative random function $c_\zs{t}$ and the capital of the
insurance company is invested in a risky asset whose price follows a geometric
Brownian motion with mean return $a$ and volatility $\sigma>0$. If
$\beta:=2a/\sigma^2-1>0$ we find exact the asymptotic upper and lower bounds
for the ruin probability $\Psi(u)$ as the initial endowment $u$ tends to
infinity, i.e. we show that $C_*u^{-\beta}\le\Psi(u)\le C^*u^{-\beta}$ for
sufficiently large $u$.
After September 2008, the advanced economies severe decline caused demand for
emerging economies' exports to drop and the crisis became truly global, much
deeper and broader than expected. In these times of global depression, most
countries and companies are affected, some more than others. The financial
crisis has turned out to be much deeper and broader than expected. Entering new
markets has always been a hazardous entrepreneurial attempt, but also a
rewarding one, in the case of success.
The problem of quantile hedging for multiple assets derivatives in the
Black-Scholes model with correlation is considered. Explicit formulas for the
probability maximizing function and the cost reduction function are derived.
Applicability of the results for the widely traded derivatives as digital,
quantos, outperformance and spread options is shown.
A new notion of stochastic ordering is introduced to compare multivariate
stochastic risk models with respect to extreme portfolio losses. In the
framework of multivariate regular variation comparison criteria are derived in
terms of ordering conditions on the spectral measures, which allows for
analytical or numerical verification in practical applications. Additional
comparison criteria in terms of further stochastic orderings are derived.
Under the Basel II standards, the Operational Risk (OpRisk) advanced
measurement approach allows a provision for reduction of capital as a result of
insurance mitigation of up to 20%. This paper studies the behaviour of
different insurance policies in the context of capital reduction for a range of
possible extreme loss models and insurance policy scenarios in a multi-period,
multiple risk settings.
In this paper we present a theoretical framework for studying coherent
acceptability indices in a dynamic setup. We study dynamic coherent
acceptability indices and dynamic coherent risk measures, and we establish a
duality between them. We derive a representation theorem for dynamic coherent
risk measures in terms of so called dynamically consistent sequence of sets of
probability measures. Based on these results, we give a specific construction
of dynamic coherent acceptability indices.
If the probability of default parameters (PDs) fed as input into a credit
portfolio model are estimated as through-the-cycle (TTC) PDs stressed market
conditions have little impact on the results of the capital calculations
conducted with the model. At first glance, this is totally different if the PDs
are estimated as point-in-time (PIT) PDs. However, it can be argued that the
reflection of stressed market conditions in input PDs should correspond to the
use of reduced correlation parameters or even the removal of correlations in
the model.
The claim experience of the past is a very important information to calculate
the fair price of an insurance contract. In a lot of European countries for
instance the prices for motor car insurance depend on the number of claims the
driver has reported to the insurance company during the last years. Classically
these prices are calculated on the basis of a mixed Poisson model with a gamma
mixing distribution. The mixing distribution models the car drivers' qualities
across the insured portfolio.
Within the context of risk integration, we introduce in risk measurement
stochastic holding period (SHP) models. This is done in order to obtain a
`liquidity-adjusted risk measure' characterized by the absence of a fixed time
horizon. The underlying assumption is that - due to changes on market liquidity
conditions - one operates along an `operational time' to which the P&L process
of liquidating a market portfolio is referred. This framework leads to a
mixture of distributions for the portfolio returns, potentially allowing for
skewness, heavy tails and extreme scenarios.
In practice daily volatility of portfolio returns is transformed to longer
holding periods by multiplying by the square-root of time which assumes that
returns are not serially correlated. Under this assumption this procedure of
scaling can also be applied to contributions to volatility of the assets in the
portfolio. Trading at exchanges located in different time zones can lead to
significant serial cross-correlations of the returns of these assets when using
close prices as is usually done in practice. These serial correlations cause
the square-root-of-time rule to fail.
Financial leverage can be regarded as an object of choice or a decision. We
show how this optics allows perceiving the recently introduced metrics of
see-through-leverage, which proved to be very useful in understanding the
phenomenology of the recent economic crisis.
We consider an optimal control problem of a property insurance company with
proportional reinsurance strategy. The insurance business brings in catastrophe
risk, such as earthquake and flood. The catastrophe risk could be partly
reduced by reinsurance. The management of the company controls the reinsurance
rate and dividend payments process to maximize the expected present value of
the dividends before bankruptcy. This is the first time to consider the
catastrophe risk in property insurance model, which is more realistic.
The paper is motivated by a problem concerning the monotonicity of insurance
premiums with respect to their loading parameter: the larger the parameter, the
larger the insurance premium is expected to be. This property, usually called
loading monotonicity, is satisfied by premiums that appear in the literature.
The increased interest in constructing new insurance premiums has raised a
question as to what weight functions would produce loading-monotonic premiums.
In this paper we demonstrate a decisive role of log-supermodularity in
answering this question.
In modern portfolio theory, the balancing of expected returns on investments
against uncertainties in those returns is aided by the use of utility
functions. The Kelly criterion offers another approach, rooted in information
theory, that always implies logarithmic utility. The two approaches seem
incompatible, too loosely or too tightly constraining investors' risk
preferences, from their respective perspectives.
Analytical, free of time consuming Monte Carlo simulations, framework for
credit portfolio systematic risk metrics calculations is presented. Techniques
are described that allow calculation of portfolio-level systematic risk
measures (standard deviation, VaR and Expected Shortfall) as well as allocation
of risk down to individual transactions. The underlying model is the industry
standard multi-factor Merton-type model with arbitrary valuation function at
horizon (in contrast to the simplistic default-only case).
This paper considers an optimal control of a large company with debt
liability under bankrupt probability constraints. The company, which faces
constant liability payments and has choices to choose various
production/business policies from an available set of control policies with
different expected profits and risks, controls the business policy and dividend
payout process to maximize the expected present value of the dividends until
the time of bankruptcy. However, if the dividend payout barrier is too low to
be acceptable, it may result in the company's bankruptcy soon.
After the shocking series of bankruptcies started in 2008, the public does
not trust anymore the classical methods of assessing business risks. The global
economic severe downturn caused demand for both developed and emerging
economies' exports to drop and the crisis became truly global. However, this
current crisis offers opportunities for those companies able to play well their
cards. Entering new markets has always been a hazardous entrepreneurial
attempt, but also a rewarding one, in the case of success.
A novel dynamical model for the study of operational risk in banks is
proposed. The equation of motion takes into account the interactions among
different bank's processes, the spontaneous generation of losses via a noise
term and the efforts made by the banks to avoid their occurrence. A scheme for
the estimation of some parameters of the model is illustrated, so that it can
be tailored on the internal organizational structure of a specific bank.
One possible way of risk management for an insurance company is to develop an
early and appropriate alarm system before the possible ruin. The ruin is
defined through the status of the aggregate risk process, which in turn is
determined by premium accumulation as well as claim settlement outgo for the
insurance company. The main purpose of this work is to design an effective
alarm system, i.e. to define alarm times and to recommend augmentation of
capital of suitable magnitude at those points to prevent or reduce the chance
of ruin.
We consider the effect of recovery rates on a pool of credit assets. We allow
the recovery rate to depend on the defaults in a general way. Using the theory
of large deviations, we study the structure of losses in a pool consisting of a
continuum of types. We derive the corresponding rate function and show that it
has a natural interpretation as the favored way to rearrange recoveries and
losses among the different types. Numerical examples are also provided.
We extend the Vasi\v{c}ek loan portfolio model to a setting where liabilities
fluctuate randomly and asset values may be subject to systemic jump risk. We
derive the probability distribution of the percentage loss of a uniform
portfolio and analyze its properties. We find that the impact of liability risk
is ambiguous and depends on the correlation between the continuous aggregate
factor and the asset-liability ratio as well as on the default intensity.
The purpose of this paper is to give a selective survey on recent progress in
random metric theory and its applications to conditional risk measures.
We examine three methods of constructing correlated Student-$t$ random
variables. Our motivation arises from simulations that utilise heavy-tailed
distributions for the purposes of stress testing and economic capital
calculations for financial institutions. We make several observations regarding
the suitability of the three methods for this purpose.
For purposes of Value-at-Risk estimation, we consider three multivariate
families of heavy-tailed distributions, which can be seen as multidimensional
versions of Paretian stable and Student's t distributions allowing different
marginals to have different tail thickness. After a discussion of relevant
estimation and simulation issues, we conduct a backtesting study on a set of
portfolios containing derivative instruments, using historical US stock price
data.
This paper considers nonlinear optimal stochastic control of insurance
company with proportional reinsurance policy under small bankrupt probability
constraints. The company controls the reinsurance rate and dividend payout
process to maximize the expected present value of the dividends until the time
of bankruptcy. However, if the optimal dividend barrier is too low to be
acceptable, it will make the company result in bankruptcy soon. In addition,
although risk and return should be highly correlated, over-risking is not a
good recipe for high return.
This paper considers optimal control problem of a large insurance company
under higher standard of solvency. The company controls proportional
reinsurance rate, dividend pay-outs and investing process to maximize the
expected present value of the dividend pay-outs until the time of bankruptcy.
This paper aims at describing the optimal return function as well as the
optimal policy.
Based on a point of view that solvency and security are first, this paper
considers optimal control and financial valuation problems of a large insurance
company facing positive transaction cost asked by reinsurer. The company
controls proportional reinsurance and dividend pay-out policy to maximize the
expected present value of the dividend pay-outs until the time of bankruptcy.
The paper aims at finding explicitly value function and an optimal control
policy of the company by using stochastic analysis and PDE methods.
The framework of this paper is that of uncertainty, that is when no reference
probability measure is given. To every convex regular risk measure $\rho$ on
${\cal C}_b(\Omega)$, we associate a canonical $c_{\rho}$-class of probability
measures. Furthermore the convex risk measure admits a dual representation in
terms of a weakly relatively compact set of probability measures absolutely
continuous with respect to some probability measure belonging to the canonical
$c_{\rho}$-class.
Discrete time hedging in a complete diffusion market is considered. The hedge
portfolio is rebalanced when the absolute difference between delta of the hedge
portfolio and the derivative contract reaches a threshold level. The rate of
convergence of the expected squared hedging error as the threshold level
approaches zero is analyzed. The results hinge to a great extent on a theorem
stating that the difference between the hedge ratios normalized by the
threshold level tends to a triangular distribution as the threshold level tends
to zero.
We show that any objective risk measurement algorithm mandated by central
banks for regulated financial entities will result in more risk being taken on
by those financial entities than would otherwise be the case. Furthermore, the
risks taken on by the regulated financial entities are far more systemically
concentrated than they would have been otherwise, making the entire financial
system more fragile.
The model is aimed to discriminate the 'good' and the 'bad' companies in
Russian corporate sector based on their financial statements data (Russian
Accounting Standards). The data sample consists of 126 Russian public
companies- issuers of Ruble bonds which represent about 36% of total number of
corporate bonds issuers. 25 companies have defaulted on their debt in 2008-2009
which represent around 30% of default cases. 29% companies in the sample have
credit ratings assigned compared to 34% in the parent population. No SPV
companies were included in the sample.
Sustaining efficiency and stability by properly controlling the equity to
asset ratio is one of the most important and difficult challenges in bank
management. Due to unexpected and abrupt decline of asset values, a bank must
closely monitor its net worth as well as market conditions, and one of its
important concerns is when to raise more capital so as not to violate capital
adequacy requirements. In this paper, we model the tradeoff between avoiding
costs of delay and premature capital raising, and solve the corresponding
optimal stopping problem.
We shall provide in this paper good deal pricing bounds for contingent claims
induced by the shortfall risk with some loss function. Assumptions we impose on
loss functions and contingent claims are very mild. We prove that the upper and
lower bounds of good deal pricing bounds are expressed by convex risk measures
on Orlicz hearts. In addition, we obtain its representation with the minimal
penalty function.
The quantitative aspirations of economists and financial analysts have for
many years been based on the belief that it should be possible to build models
of economic systems - and financial markets in particular - that are as
predictive as those in physics. While this perspective has led to a number of
important breakthroughs in economics, "physics envy" has also created a false
sense of mathematical precision in some cases. We speculate on the origins of
physics envy, and then describe an alternate perspective of economic behavior
based on a new taxonomy of uncertainty.
The intention with this paper is to provide all the estimation concepts and
techniques that are needed to implement a two-phases approach to the parametric
estimation of probability of default (PD) curves. In the first phase of this
approach, a raw PD curve is estimated based on parameters that reflect
discriminatory power. In the second phase of the approach, the raw PD curve is
calibrated to fit a target unconditional PD.
We review different approaches for measuring the impact of liquidity on CDS
prices. We start with reduced form models incorporating liquidity as an
additional discount rate. We review Chen, Fabozzi and Sverdlove (2008) and
Buhler and Trapp (2006, 2008), adopting different assumptions on how liquidity
rates enter the CDS premium rate formula, about the dynamics of liquidity rate
processes and about the credit-liquidity correlation.
We analyze the errors arising from discrete readjustment of the hedging
portfolio when hedging options in exponential Levy models, and establish the
rate at which the expected squared error goes to zero when the readjustment
frequency increases.
The presence of non linear instruments is responsible for the emergence of
non Gaussian features in the price changes distribution of realistic
portfolios, even for Normally distributed risk factors. This is especially true
for the benchmark Delta Gamma Normal model, which in general exhibits
exponentially damped power law tails. We show how the knowledge of the model
characteristic function leads to Fourier representations for two standard risk
measures, the Value at Risk and the Expected Shortfall, and for their
sensitivities with respect to the model parameters.
This paper gives an overview of the theory of dynamic convex risk measures
for random variables in discrete time setting. We summarize robust
representation results of conditional convex risk measures, and we characterize
various time consistency properties of dynamic risk measures in terms of
acceptance sets, penalty functions, and by supermartingale properties of risk
processes and penalty functions.
We study the risk assessment of uncertain cash flows in terms of dynamic
convex risk measures for processes as introduced in Cheridito, Delbaen, and
Kupper (2006). These risk measures take into account not only the amounts but
also the timing of a cash flow. We discuss their robust representation in terms
of suitably penalized probability measures on the optional sigma-field. This
yields an explicit analysis both of model and discounting ambiguity. We focus
on supermartingale criteria for different notions of time consistency.