Problems In Attempting To Simulate Investment Returns

Problems in Simulating Investment Returns by David Merkel, CFA of The Aleph Blog

Simulating hypothetical future investment returns can be important for investors trying to make decisions regarding the riskiness of various investing strategies.  The trouble is that it is difficult to do right, and I rarely see it done right.  Here are some of the trouble spots:

1) You need to get the correlations right across assets.  Equity returns need to move largely but not totally together, and the same for credit spreads and equity volatility.

2) You need to model bonds from a yield standpoint and turn the yield changes into price changes.  That keeps the markets realistic, avoiding series of price changes which would imply that yields would go too high or below zero. Yield curves also need ways of getting too steep or too inverted.

3) You need to add in some momentum and weak mean reversion for asset prices.  Streaks happen more frequently than pure randomness.  Also, over the long haul returns are somewhat predictable, which brings up:

4) Valuations.  The mean reversion component of the models needs to reflect valuations, such that risky assets rarely get “stupid cheap” or stratospheric.

5) Crises need to be modeled, with differing correlations during crisis and non-crisis times.

6) Risky asset markets need to rise much more frequently than they fall, and the rises should be slower than the falls.

7) Foreign currencies, if modeled, have to be consistent with each other, and consistent with the interest rate modeling.

Anyway, those are some of the ideas that realistic simulation models need to follow, and sadly, few if any follow them all.

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David J. Merkel, CFA, FSA — 2010-present, I am working on setting up my own equity asset management shop, tentatively called Aleph Investments. It is possible that I might do a joint venture with someone else if we can do more together than separately. From 2008-2010, I was the Chief Economist and Director of Research of Finacorp Securities. I did a many things for Finacorp, mainly research and analysis on a wide variety of fixed income and equity securities, and trading strategies. Until 2007, I was a senior investment analyst at Hovde Capital, responsible for analysis and valuation of investment opportunities for the FIP funds, particularly of companies in the insurance industry. I also managed the internal profit sharing and charitable endowment monies of the firm. From 2003-2007, I was a leading commentator at the investment website RealMoney.com. Back in 2003, after several years of correspondence, James Cramer invited me to write for the site, and I wrote for RealMoney on equity and bond portfolio management, macroeconomics, derivatives, quantitative strategies, insurance issues, corporate governance, etc. My specialty is looking at the interlinkages in the markets in order to understand individual markets better. I no longer contribute to RealMoney; I scaled it back because my work duties have gotten larger, and I began this blog to develop a distinct voice with a wider distribution. After three-plus year of operation, I believe I have achieved that. Prior to joining Hovde in 2003, I managed corporate bonds for Dwight Asset Management. In 1998, I joined the Mount Washington Investment Group as the Mortgage Bond and Asset Liability manager after working with Provident Mutual, AIG and Pacific Standard Life. My background as a life actuary has given me a different perspective on investing. How do you earn money without taking undue risk? How do you convey ideas about investing while showing a proper level of uncertainty on the likelihood of success? How do the various markets fit together, telling us us a broader story than any single piece? These are the themes that I will deal with in this blog. I hold bachelor’s and master’s degrees from Johns Hopkins University. In my spare time, I take care of our eight children with my wonderful wife Ruth.