How to estimate risk in extreme market situations

March 16, 2019

Estimating portfolio risk in extreme situations means answering two questions: First, has the market entered an extreme state? Second, how are returns likely to be distributed in such an extreme state? There are three different types of models to address these questions statistically. Conventional “extreme value theory” really only answers the second question, by fitting an appropriate limiting distribution over observations that exceed a fixed threshold. “Extreme value mixture models” simultaneously estimate the threshold for extreme distributions and the extreme distribution itself. This method seems appropriate if uncertainty over threshold values is high. Finally, “changepoint extreme value mixture models” even go a step further and estimate the timing and nature of changes in extreme distributions. The assumption of changing extreme distributions across episodes seems realistic but should make it harder to apply the method out-of-sample.

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The dollar as barometer for credit market risk

March 9, 2019

The external value of the USD has become a key factor of U.S. and global credit conditions. This reflects the surge in global USD-denominated debt in conjunction with the growing importance of mutual funds as the ultimate source of loan financing. There is empirical evidence that USD strength has been correlated with credit tightening by U.S. banks. There is also evidence that this tightening arises from deteriorating secondary market conditions for U.S. corporate loans, which, in turn, are related to outflows of credit funds after USD appreciation. The outflows are a rational response to the negative balance sheet effect of a strong dollar on EM corporates in particular. One upshot is that the dollar exchange rate has become an important early indicator for credit market conditions.

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How salience theory explains the mispricing of risk

March 2, 2019

Salience theory suggests that decision makers exaggerate the probability of extreme events if they are aware of their possibility. This gives rise to subjective probability distributions and undermines conventional rationality. In particular, salience theory explains skewness preference, i.e. the overpricing of assets with a positive skew and the under-pricing of contracts with a negative skew. There is ample evidence of skewness preference, most obviously the overpayment for insurance contracts and lottery tickets. In financial markets, growth stocks with positively-skewed expected returns have historically been overpriced relative to value stocks. This is important for macro trading. For example, a specific publicly discussed disaster risk should pay an excessive premium, and short-volatility strategies in times of fear of large drawdowns for the underlying should have positive expected value.

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Understanding China’s “financial policy”

February 23, 2019

In most developed countries macroeconomic management is the domain of separate fiscal and monetary policies. In China, the focus is on “financial policy”, a combination of credit, monetary and regulatory policies with powerful direct effects on growth and stability. This “financial policy” has critically shaped the structural development of the economy, fostering particularly state-owned enterprises, heavy industry, and real estate. It has left the economy with a difficult legacy of inefficient credit allocation, bloated shadow banking, and financial systemic risk in the real estate sector. Reforms since 2016 seek to normalize China’s macroeconomic policies but have created severe tensions between the objectives of deleveraging and sufficient growth.

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Algorithmic strategies: managing the overfitting bias

February 16, 2019

The business of algorithmic trading strategies creates incentives for model overfitting and backtest embellishment: researchers must pass Sharpe ratio thresholds for their strategies to be considered, while managers lack interest in realistic simulations of ideas. Overfitting leads to bad investment decisions and underestimated risk. Sound ethical principles are the best method for containing this risk (view post here). Where these principles have been compromised one should assume that all ‘tweaks’ to the original strategy idea that are motivated by backtest improvement contribute to overfitting. Their effects can be estimated by looking at the ratio of directional ‘flips’ in the trading signal. Overfitting typically increases with the Sharpe ratio targets of the business and the scope for applying ‘tweaks’ to the strategy. Realistic strategy performance expectations should be based on a range of plausible strategy versions, not on an optimized one.

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Understanding dollar cross-currency basis

February 9, 2019

Covered interest parity is an arbitrage condition that equalizes costs of direct USD funding and of synthetic USD funding through FX swaps. Deviations are called dollar cross-currency basis and have become a common occurrence since the great financial crisis. A negative dollar basis means direct funding in USD – if accessible – is cheaper than synthetic funding via swaps. An apparent structural cause of the dollar basis has been regulatory tightening, which has increased balance sheet costs of arbitrage. Moreover, research has found several short-term factors. Thus, a negative dollar basis has been linked to aggregate USD strength, rising market volatility, deteriorating FX market liquidity, monetary tightening in the U.S. relative to other countries, and a decrease of funds in the USD money market. In most of these cases, the dollar basis represents dollar funding conditions not captured by published interest rates and is a valid trading signal.

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Why herding is the death of momentum

February 2, 2019

Momentum trading, buying winning assets and selling losing assets, is a most popular trading strategy. It relies on sluggish market adjustment, allowing the trader to follow best-informed investors before the more inert part of the market does. Herding simply means that market participants imitate each others’ actions. Herding accelerates and potentially exaggerates market adjustments. The more quickly the herd moves, the harder it becomes to follow informed leaders profitably. In a large agile herd, sluggish adjustment gives way to frequent overreaction. Momentum strategies fail. This suggests that popularity and commoditization of momentum strategies (and trend-following) are ultimately self-defying. Conditioning momentum strategies on the estimated degree of herding should produce superior investment returns.

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ECB policy framework in six basic points

January 26, 2019

The European Central Bank is one of the most powerful institutions in the world and is running a particularly complex policy framework. For macro trading and financial modelling, the following points are critical: [1] The primary policy objective is medium-term inflation, with a horizon of two years or more and symmetric aversion to deviations from a mean of just below 2%. [2] In practice, policy rate setting has followed a simple dynamic Taylor-type rule. [3] The operational framework is very broad, with a wide range of counterparties and instruments. [4] The ECB has extensive experience with four types of non-conventional policies (long-term lending operations, asset purchases, negative interest rates, and forward guidance) that jointly exercise powerful influence on financial conditions. [5] The effectiveness ECB policy depends critically on coordinated national fiscal and regulatory policies. [6] Special mechanisms have been put in place to contain redenomination risk, i.e. fears that assets might be redenominated into legacy currencies.

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Drawdown control

January 19, 2019

Containment of drawdowns and optimization of performance ratios for multi-asset portfolios is critical for trading strategies. Alas, short data series or structural changes often render estimates of covariance matrices unreliable. A popular solution is risk-parity with volatility targeting. An alternative is ‘MinMax’ drawdown control, which builds on a broad interpretation of drawdowns as maximum actual or opportunity losses from not adjusting a benchmark portfolio to a specific underlying asset. In the case of one risky and one safe asset, this boils down to managing simultaneously the risks of conventional PnL drawdowns and foregone risk returns. Optimal asset allocation depends only on aversion to different types of drawdowns. Averaging over a plausible range of aversion parameters gives a model portfolio. Empirical evidence for the case of cryptocurrencies suggests that in an environment of uncertain returns MinMax delivers better PnL return-to-drawdown ratios than conventional volatility control.

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Liquidity yields and FX

January 12, 2019

Liquidity yields are convenience yields of financial securities that typically arise from high liquidity, suitability as collateral or preferred regulatory status. New research argues that relative changes in liquidity yields on government bonds across countries have a significant impact on exchange rate dynamics. Theoretically, an unexpected increase in the liquidity yield on government bonds in country A relative to country B triggers an appreciation of the currency of A versus B in very much the same way in which an unexpected rise in the short-term interest rate differential would. Empirically, there is evidence of a significant and consistent impact of relative liquidity yield changes on exchange rate dynamics across the G10.

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