What is an Index?

To understand the use and functioning of the index derivatives markets, it is necessary to understand the underlying index. A stock index represents the change in value of a set of stocks, which constitute the index. A market index is very important for the market players as it acts as a barometer for market behavior and as an underlying in derivative instruments such as index futures.
The Sensex and Nifty
In India the most popular indices have been the BSE Sensex and S&P CNX Nifty. The BSE Sensex has 30 stocks comprising the index which are selected based on market capitalization, industry representation, trading frequency etc. It represents 30 large well-established and financially sound companies. The Sensex represents a broad spectrum of companies in a variety of industries. It represents 14 major industry groups. Then there is a BSE national index and BSE 200. However, trading in index futures has only commenced on the BSE Sensex.
While the BSE Sensex was the first stock market index in the country, Nifty was launched by the National Stock Exchange in April 1996 taking the base of November 3, 1995. The Nifty index consists of shares of 50 companies with each having a market capitalization of more than Rs 500 crore.
Futures and stock indices
For understanding of stock index futures a thorough knowledge of the composition of indexes is essential. Choosing the right index is important in choosing the right contract for speculation or hedging. Since for speculation, the volatility of the index is important whereas for hedging the choice of index depends upon the relationship between the stocks being hedged and the characteristics of the index.
Choosing and understanding the right index is important as the movement of stock index futures is quite similar to that of the underlying stock index. Volatility of the futures indexes is generally greater than spot stock indexes.
Everytime an investor takes a long or short position on a stock, he also has an hidden exposure to the Nifty or Sensex. As most often stock values fall in tune with the entire market sentiment and rise when the market as a whole is rising.
Retail investors will find the index derivatives useful due to the high correlation of the index with their portfolio/stock and low cost associated with using index futures for hedging.