Also called the footsie, the Financial Times Stock Exchange 100 is a market capitalization weighted index representing the top 100 blue chip companies on the London Stock Exchange. The index is said to map more than 80% of the total capitalization in the United Kingdom. Stocks are free-float weighted to ensure that only the investable opportunity set is included within the index. . The FTSE group manages the Index, which in turn is a joint venture between the Financial Times and the London Stock Exchange.
They involve the total market capitalization of the companies weighted by their effect on the index, so the larger stocks would make more of a difference to the index as compared to a smaller market cap company. This is also called the free float method. The basic formula for any index is (be it capitalization weighted or any other stock index):
The Free float Adjustment factor represents the proportion of shares that is freefloated as a percentage of issued shares and then its rounded up to the nearest mulitple of 5% for calculation purposes. To find the free-float capitalization of a company, first find its market cap (number of outstanding shares x share price) then multiply its free-float factor. The free-float method, therefore, does not include restricted stocks, such as those held by company insiders.
While one might track this portfolio’s value in dollar terms, it would probably be an unwieldy number – for example, the S&P 500 market value is roughly $11.8 trillion. Rather than deal with ten or more digits, the figure is scaled to a more easily handled number, currently around 1250. Dividing the portfolio market value by a factor, usually called the Index divisor, does the scaling.
Continuity in index values is maintained by adjusting the divisor for all changes in the constituents’ share capital after the base date. This includes additions and deletions to the index, rights issues, share buybacks and issuances, and spin-offs. The divisor’s time series is, in effect, a chronological summary of all changes affecting the base capital of the index. The divisor is adjusted such that the index value at an instant just prior to a change in base capital equals the index value at an instant immediately following that change.
The List of companies that comprise the FTSE as of 16th September 2011