An investigation of hypothetical variance-covariance matrix stress-testing

Quintin Rayer

Journal of Risk Management in Financial Institutions, 2016, vol. 9, issue 3, 264-288

Abstract: Attempting to put meaningful numbers to portfolio risks is challenging. Conventional risk measures are considered often not to fully capture all risks inherent in a portfolio, particularly under difficult market conditions. Under such conditions stress-testing against artificial scenarios may help identify and quantify risks within a portfolio. Stress-tests also help reassure a portfolio or risk manager as to how a portfolio might respond to specific concerns. This paper investigates an example of stress-testing a portfolio of conventional assets against market risks using artificial scenarios based around changes to the portfolio variance-covariance matrix. Hypothetical variance-covariance matrix stress-tests include making changes to correlations between assets to explore impacts on portfolio risks. Portfolio correlations, however, cannot be changed arbitrarily to reflect a risk manager’s concerns without running the risk of implausible stressed returns and variance-covariance matrices that are not positive semi-definite. Different methods have been proposed in the literature to overcome this. This paper applies two such methods to a portfolio of four assets with the aim of illustrating the processes involved as well as drawing out differences in the approaches, enabling a discussion of their strengths and weaknesses.

Keywords: portfolio; stress-testing; scenarios; market-risk; diversification; correlation (search for similar items in EconPapers)
JEL-codes: E5 G2 (search for similar items in EconPapers)
Date: 2016
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Persistent link: https://EconPapers.repec.org/RePEc:aza:rmfi00:y:2016:v:9:i:3:p:264-288

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