Beta Instability and Implications for Hedging Systematic Risk: Takeaways from the COVID-19 Crisis
以COVID-19危机为例，揭示股票贝塔不稳定性的两个被忽视的维度，并比较几种对冲系统性风险的方法，发现优化投资组合方法可将危机期间最差日回报和波动率降低60%以上。
The authors use the COVID-19 crisis as an example to highlight two dimensions of beta instability that have been largely overlooked: First, the relative order in stock betas could change drastically when entering a crisis as the nature of market risk shifts. Second, although the relative order in beta may remain stable throughout a crisis, the absolute market risk sensitivity could also display significant changes from day to day in how individual stock returns react to the market news. These two dimensions of beta instability pose challenges for risk hedging. The authors compare the efficacy of a few approaches that hedge this systematic risk. Using a generic momentum portfolio as an illustration, the authors find that an optimized portfolio approach that maximizes/minimizes the momentum signal while matching the beta and sector exposures of the long and short legs can reduce the worst daily return and the volatility during the COVID-19 crisis by more than 60%. Their findings extend beyond this crisis period and can help investors address beta instability and hedging more broadly. <bold>TOPICS:</bold> <ext-link>Security analysis and valuation</ext-link>, <ext-link>quantitative methods</ext-link>, <ext-link>risk management</ext-link>, <ext-link>financial crises and financial market history</ext-link> <bold>Key Findings</bold> <list><list-item> ▪ Both sector beta and relative riskiness of individual stocks within a sector could be unstable, as evidenced in the COVID-19 crisis. </list-item><list-item> ▪ The magnitude of systematic reaction could also change from day to day. </list-item><list-item> ▪ An optimized portfolio approach proves flexible and efficient in hedging systematic risk exposures. </list-item></list>