Capitalization-weighted index

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A capitalization-weighted (or cap-weighted) index, also called a market-value-weighted index is a stock market index whose components are weighted according to the total market value of their outstanding shares. Every day an individual stock's price changes and thereby changes a stock index's value. The impact that individual stock's price change has on the index is proportional to the company's overall market value (the share price multiplied by the number of outstanding shares), in a capitalization-weighted index. In other types of indices, different ratios are used.

For example, the NYSE Amex Composite Index (XAX) is composed of all of the securities traded on the exchange including stocks and American depositary receipts (ADRs). The weighting of each component shifts with changes to each securities' price and the number of shares outstanding. The index moves in line with changes in price of the component.^[1][2]

Stock market indices are a type of economic index.