An index fund's rules of construction clearly identify the type of companies suitable for the fund. The most commonly known index fund in the United States, the S&P 500 Index Fund, is based on the rules established by S&P Dow Jones Indices for their S&P 500 Index. Equity index funds would include groups of stocks with similar characteristics such as the size, value, profitability and/or the geographic location of the companies. A group of stocks may include companies from the United States, Non-US Developed, emerging markets or Frontier Market countries. Additional index funds within these geographic markets may include indexes of companies that include rules based on company characteristics or factors, such as companies that are small, mid-sized, large, small value, large value, small growth, large growth, the level of gross profitability or investment capital, real estate, or indexes based on commodities and fixed-income. Companies are purchased and held within the index fund when they meet the specific index rules or parameters and are sold when they move outside of those rules or parameters. Think of an index fund as an investment utilizing rules-based investing. Some index providers announce changes of the companies in their index before the change date and other index providers do not make such announcements.
As of 2014, index funds made up 20.2% of equity mutual fund assets in the US. Index domestic equity mutual funds and index-based exchange-traded funds (ETFs), have benefited from a trend toward more index-oriented investment products. From 2007 through 2014, index domestic equity mutual funds and ETFs received $1 trillion in net new cash, including reinvested dividends. Index-based domestic equity ETFs have grown particularly quickly, attracting almost twice the flows of index domestic equity mutual funds since 2007. In contrast, actively managed domestic equity mutual funds experienced a net outflow of $659 billion, including reinvested dividends, from 2007 to 2014.
Bogle started the First Index Investment Trust on December 31, 1975. At the time, it was heavily derided by competitors as being "un-American" and the fund itself was seen as "Bogle's folly". In the first five year of Bogle's company, it made 17 million dollars. Fidelity Investments Chairman Edward Johnson was quoted as saying that he "[couldn't] believe that the great mass of investors are going to be satisfied with receiving just average returns". Bogle's fund was later renamed the Vanguard 500 Index Fund, which tracks the Standard and Poor's 500 Index. It started with comparatively meager assets of $11 million but crossed the $100 billion milestone in November 1999; this astonishing increase was funded by the market's increasing willingness to invest in such a product. Bogle predicted in January 1992 that it would very likely surpass the Magellan Fund before 2001, which it did in 2000.
Frederick L. A. Grauer at Wells Fargo harnessed McQuown and Booth's indexing theories, which led to Wells Fargo's pension funds managing over $69 billion in 1989 and over $565 billion in 1998. In 1996, Wells Fargo sold its indexing operation to Barclays Bank of London, which it operated under the name Barclays Global Investors (BGI). Blackrock, Inc. acquired BGI in 2009; the acquisition included BGI's index fund management (both its institutional funds and its iShares ETF business) and its active management.
Tracking can be achieved by trying to hold all of the securities in the index, in the same proportions as the index. Other methods include statistically sampling the market and holding "representative" securities. Many index funds rely on a computer model with little or no human input in the decision as to which securities are purchased or sold and are thus subject to a form of passive management.
Index funds are available from many investment managers. Some common indices include the S&P 500, the Nikkei 225, and the FTSE 100. Less common indexes come from academics like Eugene Fama and Kenneth French, who created "research indexes" in order to develop asset pricing models, such as their Three Factor Model. The Fama–French three-factor model is used by Dimensional Fund Advisors to design their index funds. Robert Arnott and Professor Jeremy Siegel have also created new competing fundamentally based indexes based on such criteria as dividends, earnings, book value, and sales.
Synthetic indexing is a modern technique of using a combination of equity index futures contracts and investments in low risk bonds to replicate the performance of a similar overall investment in the equities making up the index. Although maintaining the future position has a slightly higher cost structure than traditional passive sampling, synthetic indexing can result in more favourable tax treatment, particularly for international investors who are subject to U.S. dividend withholding taxes. The bond portion can hold higher yielding instruments, with a trade-off of corresponding higher risk, a technique referred to as enhanced indexing.
Because the composition of a target index is a known quantity, relative to actively managed funds, it costs less to run an index fund. Typically expense ratios of an index fund range from 0.10% for U.S. Large Company Indexes to 0.70% for Emerging Market Indexes. The expense ratio of the average large cap actively managed mutual fund as of 2015 is 1.15%. If a mutual fund produces 10% return before expenses, taking account of the expense ratio difference would result in an after expense return of 9.9% for the large cap index fund versus 8.85% for the actively managed large cap fund.
Style drift occurs when actively managed mutual funds go outside of their described style (i.e., mid-cap value, large cap income, etc.) to increase returns. Such drift hurts portfolios that are built with diversification as a high priority. Drifting into other styles could reduce the overall portfolio's diversity and subsequently increase risk. With an index fund, this drift is not possible and accurate diversification of a portfolio is increased.