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His findings were both robust to various tests and statistically significant at the 5% level (and even the 1% level in most cases). The finding on diminishing returns to scale in the fund industry is consistent with both prior research and theory. Vidal-García concluded that his “study of mutual fund performance and fund size confirms the evidence that total net assets value influence fund performance.”
Let’s examine the theory behind the diseconomies of scale. Jonathan Berk, a professor at the University of California, Berkeley, in his “must-read” paper, Five Myths of Active Portfolio Management, suggested the following thought process: “Who gets money to manage? Well, as investors know who the skilled managers are, money will flow to the best manager first. Eventually, this manager will receive so much money that it will impact the manager’s ability to generate superior returns, and expected return will be driven down to the second-best manager’s expected return. At that point, investors will be indifferent between investing with either manager, so funds will flow to both managers until their expected returns are driven down to the third-best manager. This process will continue until the expected return of investing with any manager is driven down to the expected return investors can expect to receive by investing in a passive strategy of similar riskiness (the benchmark expected return). At this point, investors are indifferent between investing with active managers or just indexing, and an equilibrium is achieved.”
Berk went on to point out that the manager with the most skill ends up with the most money. He then added, “When capital is supplied competitively by investors but ability is scarce, only participants with the skill in short supply can earn economic rents. Investors who choose to invest with active managers cannot expect to receive positive excess returns on a risk-adjusted basis.” If they did, “there would be an excess supply of capital” to those managers.
This is an important insight. Just as the efficient markets hypothesis explains why investors cannot use publicly available information to beat the market (because all investors have access to that information and, therefore, it is already incorporated in prices), the same is true of active managers. Investors shouldn’t expect to outperform the market through the use of publicly available information to select active managers. Any excess return will go to the active manager (in the form of higher expenses).
As Berk explains, the process is simple. Investors observe benchmark-beating results and funds flow into the top performers. The investment inflow eliminates return persistence because fund managers face diminishing returns to scale.
Roger Edelen, Richard Evans, and Gregory Kadlec, who authored the 2007 study Scale Effects in Mutual Fund Performance: The Role of Trading Costs, provided evidence supporting the logic of Berk’s theory. They examined the role of trading costs as a source of diseconomies of scale for mutual funds. They studied the annual trading costs for 1,706 U.S. equity funds during the period from 1995 through 2005 and found:
The authors concluded: “Our evidence directly establishes scale effects in trading as a source of diminishing returns to scale from active management.”
There is, however, another reason successful active management sows the seeds of its own destruction. As a fund’s assets grow, either trading costs will rise or the fund will have to diversify across additional securities to limit trading costs. The more a fund diversifies, the more it looks and performs like its benchmark index. It becomes what is known as a closet index fund. If it chooses this alternative, then the fund’s higher total costs have to be spread across a smaller amount of differentiated holdings, increasing the hurdle of outperformance.
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