As a consequence, capitalization-weighting has been subject to severe criticism (see e.g. Haugen and Baker 1991, Amenc, Goltz, and Le Sourd 2006, or Hsu 2006), pointing out that the mechanics of capitalization-weighting lead to trend-following strategies that provide an inefficient risk-return trade-off.
Also, while capitalization-weighting is the standard in equity index construction, different weighting schemes exist. First, while most indices use capitalization-weighting, additional criteria are often taken into account, such as sales/revenue and net income (see the “Guide to the Dow Jones Global Titan 50 Index”, January 2006). Second, as an answer to the critiques of capitalization-weighting, equity indices with different weighting schemes have emerged, such as "wealth"-weighted (Morris, 1996), “fundamental”-weighted (Arnott, Hsu and Moore 2005), “diversity”-weighted (Fernholz, Garvy, and Hannon 1998) or equal-weighted indices.
[edit] Indices and passive investment management
There has been an accelerating trend in recent decades to create passively managed mutual funds that are based on market indices, known as index funds. Advocates claim that index funds routinely beat a large majority of actively managed mutual funds; one study[citation needed] claimed that over time, the average actively managed fund has returned 1.8% less than the S&P 500 index - a result nearly equal to the average expense ratio of mutual funds (fund expenses are a drag on the funds' return by exactly that ratio). Since index funds attempt to replicate the holdings of an index, they obviate the need for — and thus many costs of — the research entailed in active management, and have a lower churn rate (the turnover of securities which lose fund managers' favor and are sold, with the attendant cost of commissions and capital gains taxes).
Indices are also a common basis for a related type of investment, the exchange-traded fund or ETF. Unlike an index fund, which is priced daily, an ETF is priced continuously, is optionable, and can be sold short.
[edit] Ethical stock market indices
A notable specialised index type is those for ethical investing indices that include only those companies satisfying ecological or social criteria, e.g. those of The Calvert Group, KLD, FTSE4Good Index, Dow Jones Sustainability Index and Wilderhill Clean Energy Index.
In 2010, the OIC announced the initiation of a stock index that complies with Islamic law's ban on alcohol, tobacco and gambling. Other such equities, such as the Dow Jones Islamic Market World Index, already exist.[7]
Another important trend is strict mechanical criteria for inclusion and exclusion to prevent market manipulation, e.g. in Canada when Nortel was permitted to rise to over 30% of the TSE 300 index value. Ethical indices have a particular interest in mechanical criteria, seeking to avoid accusations of ideological bias in selection, and have pioneered techniques for inclusion and exclusion of stocks based on complex criteria. Another means of mechanical selection is mark-to-future methods that exploit scenarios produced by multiple analysts weighted according to probability, to determine which stocks have become too risky to hold in the index of concern.
Critics of such initiatives argue that many firms satisfy mechanical "ethical criteria", e.g. regarding board composition or hiring practices, but fail to perform ethically with respect to shareholders, e.g. Enron. Indeed, the seeming "seal of approval" of an ethical index may put investors more at ease, enabling scams. One response to these criticisms is that trust in the corporate management, index criteria, fund or index manager, and securities regulator, can never be replaced by mechanical means, so "market transparency" and "disclosure" are the only long-term-effective paths to fair markets.