The Perception of Time, Risk and Return During Periods of Speculation

37 Pages Posted: 11 Jan 2002  

Emanuel Derman

Columbia University

Date Written: January 2002

Abstract

What return should you expect when you take on a given amount of risk? How should that return depend upon other people's behavior? What principles can you use to answer these questions? In this paper, we approach these topics by exploring the consequences of two simple hypotheses about risk.

The first is a common-sense invariance principle: assets with the same perceived risk must have the same expected return. It leads directly to the well-known Sharpe ratio and the classic risk-return relationships of Arbitrage Pricing Theory and the Capital Asset Pricing Model.

The second hypothesis concerns the perception of time. We conjecture that in times of speculative excitement, short-term investors may instinctively imagine stock prices to be evolving in a time measure different from that of calendar time. They may perceive and experience the risk and return of a stock in intrinsic time, a dimensionless time scale that counts the number of trading opportunities that occur, but pays no attention to the calendar time that passes between them.

Applying the first hypothesis in the intrinsic time measure suggested by the second, we derive an alternative set of relationships between risk and return. Its most noteworthy feature is that, in the short-term, a stock's trading frequency affects its expected return. We show that short-term stock speculators will expect returns proportional to the temperature of a stock, where temperature is defined as the product of the stock's traditional volatility and the square root of its trading frequency. Furthermore, we derive a modified version of the Capital Asset Pricing Model in which a stock's excess return relative to the market is proportional to its traditional beta multiplied by the square root of its trading frequency.

We hope that this model will have some relevance to the behavior of investors expecting inordinate returns in highly speculative markets.

Keywords: Risk, Return, Speculation, Capital Asset Pricing Model, Arbitrage Pricing Theory, Options Pricing, Skew, Smile, Intrinsic Time, Subordinated Processes, Internet stocks

JEL Classification: D40, D50, D81, D84, E32, G00, G110, G120, G130

Suggested Citation

Derman, Emanuel, The Perception of Time, Risk and Return During Periods of Speculation (January 2002). Available at SSRN: https://ssrn.com/abstract=296401 or http://dx.doi.org/10.2139/ssrn.296401

Emanuel Derman (Contact Author)

Columbia University ( email )

3022 Broadway
New York, NY 10027
United States
212 854 9883 (Phone)

HOME PAGE: www.ederman.com

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