Simple approximations for option pricing under mean reversion and stochastic volatility

This paper provides simple approximations for evaluating option prices and implied volatilities under stochastic volatility. Simple recursive formulae are derived that can easily be implemented in spreadsheets. The traditional random walk assumption, dominating in the analysis of financial markets, is compared with mean reversion which is often more relevant in commodity markets. Deterministic components in the mean and volatility are taken into consideration to allow for seasonality, another frequent aspect of commodity markets. The stochastic volatility is suitably modelled by GARCH. An application to electricity options shows that the choice between a random walk and a mean reversion model can have strong effects for predictions of implied volatilities even if the two models are statistically close to each other.seasonality;stochastic volatility;derivatives;mean reversion;energy markets;spreadsheets

Analytical quasi maximum likelihood inference in multivariate volatility models

Quasi maximum likelihood estimation and inference in multivariate volatility models remains a challenging computational task if, for example, the dimension is high. One of the reasons is that typically numerical procedures are used to compute the score and the Hessian, and often they are numerically unstable. We provide analytical formulae for the score and the Hessian and show in a simulation study that they clearly outperform numerical methods. As an example, we use the popular BEKK-GARCH model, for which wederive first and second order derivatives.multivariate GARCH models;quasi maximum likelihood

Estimation of temporally aggregated multivariate GARCH models

This paper investigates the performance of quasi maximum likelihood (QML) and nonlinear least squares (NLS) estimation applied to temporally aggregated GARCH models.Since these are known to be only weak GARCH, the conditional variance of the aggregated process is in general not known. Thus, one major condition that is often used in proving the consistency of QML, the correct specification of the first two moments, is absent. Indeed, our results suggest that QML is not consistent, with asubstantial bias if both the initial degree of persistence and the aggregation level are high. In other cases, QML might be taken as an approximation with only a small bias. Based on results for univariate GARCH models, NLS is likely to be consistent, although inefficient, for weak GARCH models. Our simulation study reveals that NLS does not reduce the bias of QML in considerably large samples. As the variation of NLS estimates is much higher than that of QML, one would clearly prefer QML in most practical situations. An empirical example illustrates some of the results.multivariate GARCH;temporal aggregation;weak GARCH

A generalized dynamic conditional correlation model for many asset returns

In this paper we put forward a generalization of the Dynamic Conditional Correlation (DCC) Model of Engle (2002). Our model allows for asset-specific correlation sensitivities, which is useful in particular if one aims to summarize a large number of asset returns. The resultant GDCC model is considered for daily data on 18 German stock returns, which are all included in the DAX, and for 25 UK stock returns in the FTSE. We find convincing evidence that the GDCC model improves on the DCC model and also on the CCC model of Bollerslev (1990).multivariate GARCH;dynamic conditional correlation

Testing for causality in variance using multivariate GARCH models

Tests of causality in variance in multiple time serieshave been proposed recently, based on residuals of estimatedunivariate models. Although such tests are applied frequentlylittle is known about their power properties. In this paper weshow that a convenient alternative to residual based testing is tospecify a multivariate volatility model, such as multivariateGARCH (or BEKK), and construct a Wald test on noncausality invariance. We compare both approaches to testing causality invariance in terms of asymptotic and finite sample properties. TheWald test is shown to have superior power properties under asequence of local alternatives. Furthermore, we show by simulationthat the Wald test is quite robust to misspecification of theorder of the BEKK model, but that empirical power decreasessubstantially when asymmetries in volatility are ignored.causality;local power;multivariate volatility

Semiparametric multivariate volatility models

Estimation of multivariate volatility models is usually carried out by quasi maximum likelihood (QMLE), for which consistency and asymptotic normality have been proven under quite general conditions. However, there may be a substantial efficiency loss of QMLE if the true innovation distribution is not multinormal. We suggest a nonparametric estimation of the multivariate innovation distribution, based on consistent parameter estimates obtained by QMLE. We show that under standard regularity conditions the semiparametric efficiency bound can be attained. Without reparametrizing the conditional covariance matrix (which depends on the particular model used), adaptive estimation is not possible. However, in some cases the efficiency loss of semiparametric estimationwith respect to full information maximum likelihood decreases as the dimension increases.In practice, one would like to restrict the class of possible density functions to avoid the curse of dimensionality. One way of doing so is to impose the constraint that the density belongs to the class of spherical distributions, for which we also derive the semiparametric efficiency bound and an estimator that attains this bound. A simulation experiment demonstrates the efficiency gain of the proposed estimator compared with QMLE.

Testing for vector autoregressive dynamics under heteroskedasticity

In this paper we introduce a bootstrap procedure to test parameterrestrictions in vector autoregressive models which is robust incases of conditionally heteroskedastic error terms. The adoptedwild bootstrap method does not require any parametricspecification of the volatility process and takes contemporaneouserror correlation implicitly into account. Via a Monte Carloinvestigation empirical size and power properties of the newmethod are illustrated. We compare the bootstrap approach withstandard procedures either ignoring heteroskedasticity or adoptinga heteroskedasticity consistent estimation of the relevantcovariance matrices in the spirit of the White correction. Interms of empirical size the proposed method clearly outperformscompeting approaches without paying any price in terms of sizeadjusted power. We apply the alternative tests to investigate thepotential of causal relationships linking daily prices of naturalgas and crude oil. Unlike standard inference ignoring time varyingerror variances, heteroskedasticity consistent test procedures donot deliver any evidence in favor of short run causality betweenthe two series.Energy markets;Causality;Bootstrap;Heteroskededasticity;Hypothesis testing;Vector autoregression

Ridge regression revisited

We argue in this paper that general ridge (GR) regression implies no major complication compared with simple ridge regression. We introduce a generalization of an explicit GR estimator derived by Hemmerle and by Teekens and de Boer and show that this estimator, which is more conservative, performs better than the Hoerl and Kennard estimator in terms of a weighted quadratic loss criterion.general ridge estimator;MSE performance

Multivariate mixed normal conditional heteroskedasticity

We propose a new multivariate volatility model where the conditional distribution of a vector time series is given by a mixture of multivariate normal distributions. Each of these distributions is allowed to have a time-varying covariance matrix. The process can be globally covariance-stationary even though some components are not covariance-stationary. We derive some theoretical properties of the model such as the unconditional covariance matrix and autocorrelations of squared returns. The complexity of the model requires a powerful estimation algorithm. In a simulation study we compare estimation by a maximum likelihood with the EM algorithm and Bayesian estimation with a Gibbs sampler. Finally, we apply the model to daily U.S. stock returns.Multivariate volatility; Finite mixture; EM algorithm; Bayesian inference

Simple approximations for option pricing under mean reversion and stochastic volatility

This paper provides simple approximations for evaluating option prices and implied volatilities under stochastic volatility. Simple recursive formulae are derived that can easily be implemented in spreadsheets. The traditional random walk assumption, dominating in the analysis of financial markets, is compared with mean reversion which is often more relevant in commodity markets. Deterministic components in the mean and volatility are taken into consideration to allow for seasonality, another frequent aspect of commodity markets. The stochastic volatility is suitably modelled by GARCH. An application to electricity options shows that the choice between a random walk and a mean reversion model can have strong effects for predictions of implied volatilities even if the two models are statistically close to each other