Practical analysis for investment professionals
11 June 2024

FX Bubbles: Through the Lens of Shiller and Sornette

It is widely understood that psychological factors such as perceptions and herd mentality can significantly influence stock market dynamics and precipitate speculative bubbles and abrupt market corrections. Less appreciated is the fact that the foreign exchange (FX) market is equally susceptible to such risks and perhaps more so in the context of geopolitical events.

The FX market — an over-the-counter marketplace that sets exchange rates for currencies worldwide — is the largest market globally in terms of trading volume. We’re going to look at bubbles in the FX market through the lens of Robert Shiller and Didier Sornette.

A notable example of an FX market bubble and crash is the case of the Icelandic króna during the early 2000s. The króna appreciated significantly following the deregulation of Iceland’s financial sector in 2001, which allowed financial institutions to expand and facilitated greater foreign investment. This financial-sector expansion, combined with Iceland’s high interest rates, attracted considearble speculative investment as herd mentality settled in.

In early 2007, The Economist ranked the Icelandic króna as the most overvalued currency based on its Big Mac Index. The bubble burst during the global financial crisis of 2008, resulting in a severe depreciation of the króna and a dramatic economic collapse for Iceland.

Shiller Challenges Neoclassical Models

When speaking about price bubbles in any asset class, it is essential to start with Shiller’s theories and then move onto Sornette’s models. Shiller’s insights into financial market dynamics challenge traditional neoclassical models and offer a deeper understanding of purely speculative price runups that can be applied to FX markets. His theories, particularly the Excess Volatility Hypothesis, suggest that just like stock markets, the FX market might experience volatility that exceeds what could be justified by economic fundamentals such as interest rates, inflation rates, or balance of payments.

Shiller’s integration of behavioural finance into the analysis of financial markets underscores the significant role of psychological factors in trading and investment decisions. In the FX market, this could manifest as currency values being influenced by perceptions, herd behaviour, and overreactions to news — factors that can drive the market away from fundamental values and potentially lead to speculative bubbles and abrupt corrections.

Questioning the efficient market hypothesis, Shiller proposes that markets may not always efficiently incorporate new information, a theory applicable to FX markets. Anomalies such as predictable patterns from carry trade opportunities suggest that FX markets, similar to stock markets, exhibit moments where past pricing data could help predict future movements.

Shiller advocates for a broader approach to understanding financial markets, one that includes non-economic factors such as geopolitics, market sentiment, and economic events. These factors can influence currency prices and induce large-scale speculative movements, akin to bubbles seen in other financial markets.

Shiller’s theories provide a framework for understanding the FX market that goes beyond classical economic analysis, incorporating the interplay of economic, psychological, and sociological factors. This comprehensive approach challenges the purely rational and efficient market paradigm and highlights the need for a nuanced view of FX dynamics. This broader perspective is crucial for predicting and understanding the subtleties of currency fluctuations and the often-irrational behaviour of market participants.

Enter Sornette: A Model to Predict Bubbles

When measuring bubbles, Sornette inevitably comes to mind. The researcher explores the phenomena of financial crashes and the dynamics of capital markets. He delves into the patterns and behaviours that lead to market failures, focusing on the critical concept of bubbles. Unlike traditional definitions, which rely on comparing an asset’s price with its often difficult-to-measure fundamental value, a financial bubble in this context is characterized by the detection of unsustainable movement in the asset’s price.

A key theme of Sornette’s research is the predictability of financial crashes. He argues that while markets often appear random and driven by myriad factors, they can sometimes exhibit patterns that signal an impending crash. One of the primary methods Sornette developed for identifying such patterns is the Log-Periodic Power Law Singularity (LPPLS) model.

The LPPLS model posits that financial bubbles can be detected through the identification of two important components: 1) faster-than-exponential growth of the asset price during the formation of the bubble, and 2) accelerating oscillations in prices as they approach a critical point, essentially capturing how market sentiment escalates before a crash.

In applying this model to the FX market, Sornette suggests that similar patterns may be observable in currencies. FX markets, like stock markets, are influenced by a combination of macroeconomic variables, geopolitical events, and trader psychology. The LPPLS model can potentially help in identifying bubbles in FX markets by analysing the super-exponential growth and log-periodic oscillations in exchange rates. If such patterns are found, they can serve as early warning signs of an impending significant adjustment or crash in the currency values.

For instance, before a currency crashes, it might experience an increasingly rapid appreciation against other currencies, accompanied by a rise in speculative trading and investment in that currency market. This could create an unsustainable bubble that eventually bursts, leading to a sharp adjustment in the price. By monitoring such rapid growth and price oscillations and using statistical tools to analyse their frequency and magnitude, investors and economists can potentially predict and mitigate the adverse effects of such crashes.

Sornette’s insights provide a theoretical foundation for considering how the complex dynamics of market behaviours and psychological factors can be modelled and understood, offering a unique lens through which to view the prediction and management of risks in the realm of FX investing.

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All posts are the opinion of the author. As such, they should not be construed as investment advice, nor do the opinions expressed necessarily reflect the views of CFA Institute or the author’s employer.

Image credit: ©Getty Images / Ascent / PKS Media Inc.


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About the Author(s)
Sebastian Petric, CFA

Sebastian Petric, CFA, is an investment professional with LGT and worked previously as a capital market researcher with Raiffeisen Bank International and as a director in the investment office of UBS. He was educated at the Vienna University of Economics and Business, the London School of Economics, and the University of Oxford. Petric has a strong interest in asset pricing, development finance, inclusive globalization, and sustainable economic growth and recently published his book, entitled Predictability of Financial Crises: The Impact of Fundamental, Policy-induced and Institutional Vulnerabilities on China Compared to other Emerging Markets.

Ming Deng, PhD

Ming Deng, PhD, is a quantitative analyst at LGT Bank. He holds a PhD from the University of Zurich and the Swiss Finance Institute, an MSc from the University of Zurich and ETH Zurich, and a bachelor's degree from Nankai University. His research interests focus on applying machine learning and using textual data to study the impact of public information on financial markets. His research work has been cited in various media outlets such as Bloomberg and NZZ.

1 thought on “FX Bubbles: Through the Lens of Shiller and Sornette”

  1. Kirk Cornwell says:

    We take for granted a working acceptance of fiat money from places whose day to day “money supply” couldn’t possibly be evaluated by traditional methods. The U.S. may be the best house on a bad block but we are rapidly “losing count” ourselves now that debt per person is in six figures. Is it nice of us to take their money, or is the world carrying us? Exchange rates are merely psychological at this point.

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