Stock market index
measures a stock market to help investors compare stock prices
In finance, a stock market index or stock index is an index that measures the performance of a stock market, or of a subset of a stock market. It helps investors compare current stock price levels with past prices to calculate market performance.
Two of the primary criteria of an index are that it is investable and transparent: The methods of its construction are specified. Investors may be able to invest in a stock market index by buying an index fund, which is structured as either a mutual fund or an exchange-traded fund, and "tracks" an index. The difference between an index fund's performance and the index, if any, is called tracking error.
Types of indices by coverage
Stock market indices may be classified and segmented by the set of underlying stocks included in the index, sometimes referred to as the "coverage". The underlying stocks are typically grouped together based on their underlying economics or underlying investor demand that the index is seeking to represent or track.
The coverage of a stock market index is separate from the weighting method. For example, the S&P 500 market-cap weighted index covers the 500 largest stocks from the S&P Total Market Index, but an equally weighted S&P 500 index is also available with the same coverage.
World or global coverage
These indices attempt to represent the performance of the global stock market.
The public source identifies “Stock market index” as measures a stock market to help investors compare stock prices. This brief keeps that definition visible, then builds a research path around Stock, market and index.
Why this record matters
A short description can identify a subject without explaining its stakes. For “Stock market index”, the useful work is to connect “measures a stock market to help investors compare stock prices” to the records capable of establishing context and consequence.
Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Sep 17, 2026. The linked authority identifier is Q223371. The Library of Congress control number is sh86007076. 1 of 1 selected statements include explicit references; 1 carry qualifiers and 0 use preferred rank.
A concise general-reference account can conceal disagreements about scope, terminology or the weight assigned to individual sources. The source lead contains qualifying language; that uncertainty should survive quotation, summary and reuse. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “Stock market index”, its source revision and the description used here.
- Expand the search: follow Stock market index primary sources, Stock market index archive and Stock research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “Stock market index”?
- Which cited source is closest to the event, object or claim?
- Which institution is responsible for the underlying evidence?
Search terms from this dossier
This entry incorporates text from “Stock market index” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.