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Does Indexing Affect Stock Prices?

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Index mutual funds have become the villains of an investment soap opera. Active managers have been blaming their underperformance on S&P 500 Index funds. The theory goes like this: money pours into the index funds because of the dissatisfaction with the underperformance of active managers; the funds "blindly" buy the large-cap stocks and drive the market ever higher.

The problem is that this theory is based on a false premise, as Melissa Brown demonstrated several years ago. Brown, then head of quantitative research at Prudential Securities, found that while S&P 500 Index funds had grown in assets from $255 billion at the end of 1992 to $600 billion at the end of 1997, they represented only 6.1 percent of all stocks by the end of 1997, down from 6.7 percent at the end of 1992. Brown pointed out that since the total return (price appreciation plus dividends) of the S&P 500 Index was 152 percent, all of the gain in the amount of S&P 500 indexed assets was a result of price appreciation, not cash inflow. In fact, if the amount of funds in S&P 500 Index funds had grown as much as the 152 percent total return of the Index itself, the amount of money invested in these funds would have grown to almost $650 billion. This is $50 billion more than they actually held. This indicates there were actually net cash outflows from these funds. This clearly suggests that the underperformance of active managers is not due to inflows into index funds. (1)

It is important to note that the net cash outflow from S&P 500 Index funds during this period should not be taken as an indication that investors were decreasing their commitment to passive investing. In fact, the contrary was true. Not all index funds are tied to the S&P 500. In recent years index funds have been created to replicate the performance of the Russell 2000, the S&P/Barra Value Index, the MSCI EAFE Index, and many others. When all passive funds are considered, their market share was growing at a rapid pace.

Burton Malkiel and Alexander Radisich took another look at the claim that indexing influences security prices. (2) Their study, "The Growth of Index Funds and the Pricing of Equity Securities," tested three hypotheses:

  1. Index funds will tend to increase their advantage over actively managed funds during periods when the market rises.
  2. S&P 500 Index funds will tend to increase their advantage over actively managed funds during periods when large-cap stocks outperform smaller firms.
  3. S&P 500 Index funds will increase their advantage as the proportion of fund inflows into index funds increases.

The first hypothesis is logical in that in rising markets index funds have the advantage of always being virtually fully invested while actively managed funds typically carry cash positions (of as much as five to ten percent, or more) for liquidity and trading purposes. The study found that the hypothesis is correct in that the excess performance of indexing increases when the market is rising. The t-stat, a measure of statistical significance, was very high at 4.9 (with 2.0 considered the hurdle for significance as it provides ninety-five percent confidence that the result was not a random outcome). It is important to note, so that you don't jump to the wrong conclusion, that indexing has also outperformed in bear markets as well.

Another theory is that by anticipating bear markets, active managers can reduce their exposure to equities and protect their investors from the type of losses that index funds experience (since index funds are always virtually one hundred percent invested). Let's look at the historical record to see if active managers actually provided the protection they claim they provide in bear markets.

  • Just prior to the worst bear market in the postwar era (1973-74), mutual fund cash reserves stood at only four percent. Cash positions reached about twelve percent at the ensuing low.
  • In mid-1998, when the Asian Contagion bear market arrived, cash reserves were just five percent. Compare this to the thirteen percent level reached at the market low in 1990, just prior to beginning the longest bull market in history. (3)

A Lipper Analytical Services study provided further evidence on the failure of active managers to outperform in bear markets. Lipper studied the six market corrections (defined as a drop of at least ten percent) from August 31, 1978, to October 11, 1990, and found that while the average loss for the S&P was 15.1 percent, the average loss for large-cap growth funds was 17.0 percent. (4)

Fund managers fared no better in the bear market of July-August 1998. The average equity fund lost 19.7 percent. This compares to losses of just 17.4 percent and 15.4 percent for a Wilshire 5000 Index fund and an S&P 500 Index fund, respectively. (5)

And, finally, consider this evidence - Goldman Sachs studied mutual fund cash holdings from 1970 to 1989. The study found that mutual fund managers miscalled all nine major turning points. (6)

It is worth noting that the commercial success of indexing among institutional investors began in 1975 (a fund was built for New York Telephone's pension plan). The poor performance of most active managers during the bear market of 1973-74, the most brutal since the 1930s, revealed how just how hollow the claim that their "expertise" in protecting capital is most valuable in difficult markets. While it may be coincidence, I suspect that the motivation to adopt indexed strategies was partly attributable to disappointment with the traditional active management approach, which failed to deliver when it was most needed.

The second hypothesis (S&P 500 Index funds will tend to increase their advantage over actively managed funds during periods when large-cap stocks outperform smaller firms) is also logical in that not all actively managed funds hold only large-cap stocks, as does the S&P 500. Thus in periods like 1991-93, when small-cap stocks outperformed large-cap stocks, we should expect that not only will small-cap funds outperform a large-cap index fund, but that also some large-cap funds will also do so (as many are not style pure, holding smaller cap stocks than are in the S&P 500 Index). This is exactly what happened during this period. The study confirmed this hypothesis as well: When small companies outperform, the advantage of indexing large-cap stocks shrinks. The t-stat again was very significant at a negative 3.2.

The third hypothesis, that indexing influences prices, is, however, rejected. They found that the flow of money into index funds was totally unrelated to the excess performance of index funds. Thus there is no support at all to the claim that the success of indexing has been self-fulfilling.

The authors also studied the impact of a stock's entry into the S&P 500 Index. There have been studies showing that a stock's entry bolsters demand and increases the average price of stocks. The study examined the price action of all stocks entering the S&P 500 Index between July 1980 and July 1999. The authors found that while there is a statistically significant post-entry "pop" lasting about one week, the excess performance is essentially reversed over the following year. This contradicts the notion that there is any permanent price impact for stocks that enter an index.

The authors also made another important observation that demonstrates the false nature of the claims that indexing influences prices and was responsible for the failure of active managers in the late 1990s. They note that the superior performance of the S&P 500 Index during this period was driven mostly by the returns of the very largest stocks in the index-the performance of the top fifty far surpassed the performance of the remaining four hundred and fifty. Because indexing purchases a proportional share (based on market capitalization) of each stock it cannot be responsible for the outperformance of the top fifty. Thus it must have been the actions of active managers that were in fact driving returns.

The evidence and the logic is that indexing does not drive prices. The advantage of indexing is based on solely on the mathematics of investing: Since someone must own all stocks, passive investors and active investors both must earn the same gross returns. And since passive investors incur lower costs, they must in aggregate earn higher net returns. Despite this logic, there are two things of which we can be sure. The first is that the next time small caps outperform large caps we will hear once again "that it is a stock-pickers market." Nothing of course could be further from the truth. It is simply an issue of understanding what is the proper benchmark to use. Small-cap fund managers, while outperforming the S&P 500 index, will be underperforming the index against which they should always be benchmarked, the S&P 600 Index (a small-cap index). The second is that in periods when large-caps outperform (and thus the S&P 500 Index will outperform the majority of active managers) the marketing machines of Wall Street will find a different excuse for their poor performance. Passive investing is the winner's game in all markets; the math dictates that it must be so.

(1) Wall Street Journal, March 11, 1998.
(2) Burton G. Malkiel and Alexander Radisich, "The Growth of Index Funds and the Pricing of Equity Securities," The Journal of Portfolio Management, Winter 2001, p. 9.
(3) John Bogle, Bogle on Investing, p. 89.
(4) Richard E. Evans and Burton G. Malkiel, The Index Fund Solution.
(5) Lipper Analytical Service.
(6) William Sherden, Fortune Sellers, p. 121.

Larry Swedroe is the author of "What Wall Street Doesn't Want You to Know" and "The Only Guide To A Winning Investment Strategy You Will Ever Need." His third book, "Rational Investing In Irrational Times, How to Avoid the Costly Mistakes Even Smart People Make Today," will be published in April 2002 by St. Martins Press. Larry is also the Director of Research for and a Principal of both Buckingham Asset Management, Inc. and BAM Advisor Services in St. Louis, Missouri. However, his opinions and comments expressed within this column are his own, and may not accurately reflect those of Buckingham Asset Management or BAM Advisor Services.