Stock market indices are traded in large volumes and are very popular in the investing community. They are not only a great place to start for beginners but are also traded by experienced professionals daily. Indices are great for day-traders and long-term traders alike. It is important for a stock market to be transparent. Transparent in what stocks are included in the index and how the index is calculated. Transparent indices are easier for ETF’s to track because they help ETF managers allocate the right weights to the different stocks in the ETF.
There are many ways to calculate the value of a stock index, but the most popular methods are:
The Market Capitalization Weighted Method whereby the stocks in the index are weighted using the market capitalization of the individual companies. The largest company in the index by market cap will generally lead to the most movement in the index. The S&P 500 is an example of a market capitalization weighted index.
The Price Weighted Method whereby the stocks in the index are weighted by the price of the stock. This can lead to companies with smaller market capitalizations but higher stock prices having a bigger effect on the overall index. The DJIA is an index weighted using the price-weighted method.
The Equal Weighted Method whereby the return of each stock in the index is calculated and then summed and divided by the amount of stocks in the index.
The Fundamental Weighted Method whereby the index is constructed using fundamental aspects like price to earnings ratios, earnings, book values and others.
Most indices are calculated using the market capitalization weighted method.