Price-weighted
Encyclopedia
A price-weighted index is a stock market index
Stock market index
A stock market index is a method of measuring a section of the stock market. Many indices are cited by news or financial services firms and are used as benchmarks, to measure the performance of portfolios such as mutual funds....

 where each constituent makes up a fraction of the index that is proportional to its price. For a stock market
Stock market
A stock market or equity market is a public entity for the trading of company stock and derivatives at an agreed price; these are securities listed on a stock exchange as well as those only traded privately.The size of the world stock market was estimated at about $36.6 trillion...

 index this implies that stock
Stock
The capital stock of a business entity represents the original capital paid into or invested in the business by its founders. It serves as a security for the creditors of a business since it cannot be withdrawn to the detriment of the creditors...

s are included in proportions based on their quoted prices. A stock trading at $100 will thus be making up 10 times more of the total index compared to a stock trading at $10. This is different from a market weighted index where stocks are included based on the equity
Stock
The capital stock of a business entity represents the original capital paid into or invested in the business by its founders. It serves as a security for the creditors of a business since it cannot be withdrawn to the detriment of the creditors...

 market values of the underlying companies, i.e. the quoted stock price multiplied by the number of shares outstanding
Shares outstanding
Shares outstanding are common shares that have been authorized, issued, and purchased by investors. They have voting rights and represent ownership in the corporation by the person or institution that holds the shares. They should be distinguished from treasury shares, which is common stock held by...

.

The development of a price-weighted index will not accurately reflect the evolution of the underlying market value
Market value
Market value is the price at which an asset would trade in a competitive auction setting. Market value is often used interchangeably with open market value, fair value or fair market value, although these terms have distinct definitions in different standards, and may differ in some...

s. This is so because the $100 stock above might be that of a small company and the $10 stock that of a large company. A change in the price quote of the small company will thus drive the price-weighted index (as it makes up a large part of the index) while the combined market values will remain relatively unaffected without changes in the price quote of the large company. Moreover, constant rebalancing needs to take place. The quoted price for each stock used in the calculation of the index is redefined so that each index constituent has an appropriate weight in the index at each rebalancing date. An Adjustment factor is introduced to a stock, that is assigned to the stock at each rebalancing date, which allows for price weighting. For index component, the value would be:
  • Adjustment Factor= Index specific constant "Z"/(Number of shares of the stock*Adjusted stock market value before rebalancing)


The Dow Jones Industrial Average
Dow Jones Industrial Average
The Dow Jones Industrial Average , also called the Industrial Average, the Dow Jones, the Dow 30, or simply the Dow, is a stock market index, and one of several indices created by Wall Street Journal editor and Dow Jones & Company co-founder Charles Dow...

 is an example of a price-weighted stock market index.

External links

  • Price-weighted calculation methodology via Wikinvest

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