Abstract
We study the robust portfolio optimization model for the Omega ratio when the joint ambiguity in the returns distributions is modeled utilizing copulas. We propose the copula formulation of the Omega ratio and use it to formulate the worst-case robust optimization model. Furthermore, we propose a Markov chain predicated filtering strategy to filter a set of fewer assets from a large pool of available assets in the market to amend the performance of the conventional Omega ratio model. We propose an R-vine copula Autoregressive Moving Average Generalized Autoregressive Conditional Heteroskedasticity (ARMA-GARCH) model for the joint distribution of assets returns. We obtain the standardized residuals for each return series of the filtered assets using the ARMA-GARCH model and, subsequently, exploit the regular vine copulas to model the joint dependence among the transformed residuals. The tree structure in the regular vines is accomplished using Kendall’s tau. The dependence structure so obtained is used to simulate scenarios for the returns of assets. The simulated data is used to obtain optimal portfolios in the worst-case Copula Omega ratio model. Empirical evidence shows the aptness of the proposed filtering strategy and analyzes the performance of the worst-case copula Omega portfolios on several datasets using a rolling window approach. The optimal portfolios from the worst-case copula Omega model are found to outperform the portfolios from the Gaussian copula Omega ratio model by having a higher information ratio, Value-at-risk ratio, and Rachev ratio.
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Notes
The choice of copulas considered for the formation of mixture copulas is inspired from Rustem ([27]) and the earlier works ([21, 22]), seen along with the research in ([19, 20]). Each chosen copula better describes different dependency. Clayton, Joe and Gumbel are non-symmetric to explain stronger dependence below and above the 50-th percentile, respectively; Frank copula is symmetric but it has different properties to the Gaussian copula. Hence, by using them in a mixture structure we can cover a large spectrum of possible dependencies.
A Naive portfolio of n assets has 1/n weight allocated to each asset.
The performance measures used are mean return, Sortino ratio (SR), standard deviation (Std Dev), downside deviation (DD), Information ratio, Omega Sharpe ratio, Sharpe ratio with standard deviation, VaR and CVaR as risk measures, VaR, CVaR, Rachev ratios, and VaR ratios, at 97 and 95% level of confidence
We first select a copula family among these five. Then determine the best pair-copula at each node amongst the various rotations of the chosen copula family which are available in the R package VineCopula. We follow this procedure with each of the five copulas.
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The first author is thankful to the Council of Scientific and Industrial Research, India, for providing the financial grant in initiating the present research and IIT Delhi for extending the financial support to conclude the same. The authors are grateful to the editor and referees for their valuable support and constructive suggestions.
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Goel, A., Mehra, A. Robust Omega ratio optimization using regular vines. Optim Lett 15, 2067–2108 (2021). https://doi.org/10.1007/s11590-020-01629-5
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DOI: https://doi.org/10.1007/s11590-020-01629-5