Avoid the Dangers of Data-Mining, Part 2

1. Black Friday's 10 Top Tech Deals 2. Motorola Droid Price Cut 3. Cramer's 'Mad Money' Recap: The Next Leg in the Housing Rally (Final) 4. Citigroup Worst of Bank Stocks, Poll Says 5. Cramer's 'Stop Trading': Verizon, AT&T

Editor's Note: This is the second installment of a two-part series. To read Part 1, please click here.

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Other Areas of Data-Mining

In 1992-1993, there were a number of bright investors who had "picked the lock" of the residential mortgage-backed securities market. Many of them had estimated complex multifactor relationships that allowed them to estimate the likely amount of mortgage prepayment within mortgage pools. Armed with that knowledge, they bought some of the riskiest securities backed by portions of the cash flows from the pools.

They probably estimated the past relationships properly, but the models failed when no-cost prepayment became common, and failed again when the Federal Reserve raised rates aggressively in 1994. The failures were astounding: David Askin's hedge funds, Orange County, the funds at Piper Jaffray that Worth Bruntjen managed, some small life insurers, etc. If that wasn't enough, there were many major financial institutions that dropped billions on this trade without failing.

What's the lesson? Models that worked well in the past might not work so well in the future, particularly at high degrees of leverage. Small deviations from what made the relationship work in the past can be amplified by leverage into huge disasters.

I recommend Victor Niederhoffer and Laurel Kenner's book, Practical Speculation, because the first half of the book is very good at debunking data-mining. But it also mines data on occasion. In Chapter 9, for example, the authors test methods to improve on buying and holding the index over long periods by adjusting position sizes based off of the results of prior years. Enough results were tested that it was likely that one of them might show something that would have worked in the past. My guess is that the significant results there are a statistical fluke and may not work in the future. The results did not work in the recent 2000-2002 downturn.

As an aside, one of the reasons Niederhoffer's hedge fund blew up is that he placed too much trust in the idea that the data could tell him what events could not happen. The market has a funny way of doing what everyone "knows" it can't, particularly when a majority of market participants rely on an event not happening. In this case, Niederhoffer knew that when U.S. banks fall by 90% in price and survive, typically they are a good value. Applying that same insight to banks in Thailand demanded too much of the data, and was fatal to his funds.

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David J. Merkel, CFA, FSA, is 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. Previously, he managed corporate bonds for Dwight Asset Management. At time of publication, neither Merkel nor his fund had any positions in the securities mentioned in this column, though positions may change at any time. Under no circumstances does the information in this column represent a recommendation to buy or sell stocks. While Merkel cannot provide investment advice or recommendations, he welcomes your feedback and invites you to send your comments to [e-mail].

Analyst Certification: All of the views expressed in the report accurately reflect the personal views of the research analyst about any and all of the subject securities or issuers. No part of the compensation of the research analyst named herein was, is, or will be, directly or indirectly, related to the specific recommendations or views expressed by the research analyst in this report.

Merkel is employed by Hovde Capital Advisors LLC (the "firm"), a registered investment advisor with its principal office located in Washington, D.C. The Firm and/or its affiliates have or may have a long or short position or holding in the securities, options on securities, or other related investments of the issuers mentioned herein.