Index Rex

September 09, 2003

V. Manage Stock Migration

Although market-cap and style-oriented bands would reduce turnover and better reflect the way active managers respond to changes in stock characteristics, there would still be those hard lines in the sand at the edges of a band. When a company crossed this edge, the stock would exit the index, and in the case of size indexes, migrate entirely from one classification to another. Once again, this is not an accurate representation of how active managers respond to secular shifts in the characteristics of a company. In reality, because managers act independently, there is no one point, or even brief period, in which they collectively decide to eliminate a stock that is leaving their investment style. One by one, they may act quickly, but as a group they remove such stocks from their portfolios gradually.

How can an index be made to reflect this reality? One way would be to divide the index into 12 equally sized subcomponents, with each subcomponent associated with a month of the year. If Stock A had a market capitalization of $12 billion, for example, each of the 12 subcomponents would contain $1 billion of Stock A. Every month, the subcomponent associated with that month would be opened up, analyzed, and reconstituted.

Figure 2 shows how this might look, using an imaginary set of indexes being reviewed in May 2002. The index sponsor has opened that month's subcomponent, which was established in May 2001, and analyzed the stocks to determine whether they still meet the index criteria. In May 2001, Stocks A, B, and C were large-cap, and Stock D small-cap. A year later, Stock C has migrated down to the small-cap category, and Stock D has migrated up to the large-cap category. The subcomponent's 1/12 position in Stock C is moved to the small-cap index, and its 1/12 position in D is moved to the large-cap index. Adjustments made in the May subcomponent have no effect on the other 11 subcomponents.

This process means that, during any one month, only 1/12 of a stock's float-adjusted market capitalization would be transferred from one index to another. At a minimum, it would take 12 months for a stock to entirely migrate from one index to another. During this transition period, the stock might be in two indexes, but the weights in the large- and small-cap indexes would be complementary. A particular stock might have 7/12ths of its weight in the large-cap index, for example, and 5/12ths in small cap.

This migration process more closely reflects how active managers invest. First, they do not, as a herd, pile into, or out of, a stock as it crosses a certain threshold. Instead, they collectively wade into and out of a position. An index that followed the same process would not only be a better benchmark, it would also benefit index fund investors by significantly reducing turnover and allowing the portfolio to be repositioned in a more orderly fashion, significantly reducing the fund's transaction costs by use of the monthly reconstitutions. The index itself would have lower embedded transaction costs, which would enhance long-term results.

It should be noted that most indexes currently lead to significant transaction costs when securities are added or subtracted. The cost of style integrity is disproportionately high for small-cap indexes, which have recently had annual turnover as high as 35% to 45%.


To create relevant benchmarks for actively-managed investments, our frame of reference should be the active managers themselves. It is these managers, not investment theory, that define growth and value, small-cap and large-cap. With indexes that mimic the thought processes of active managers, investors would have better tools for evaluating the performance of professional managers, helping them to make smarter decisions about their portfolio allocation. Consultants and researchers would also have better tools for attributing a portfolio performance to the returns of different investment styles.

A widespread misconception is that indexing works in large caps, but not in sectors such as small caps. At times, this conclusion appears to be supported by the data. But the data's real lesson is that we're measuring managers with the wrong yardsticks. With better benchmarks, outperforming-or underperforming-an index would no longer be a matter of holding stocks from a different universe. Performance would reflect the success of a manager's stock selections within the appropriate universe. Although it's unlikely that large numbers of active managers could boast of index-beating performance, even over short periods, these better indexes could in fact be a boon to talented active managers. Their relative success could be attributed to skill, not dismissed as an artifact of faulty benchmark construction.


This article originally appeared in the Q3 2003 edition of the Journal of Indexes.


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