each constituent security continue to represent an ap- proximately equal dollar value in the index without dis- torting the level of the index. Another method of calculation is simply to add up the prices of the securities in the index and divide by the number of securities in the index. disregarding numbers of shares outstanding. Another method mea- sures daily percentage movements of prices by aver- aging the percentage price changes of all securities included in the index. Investors should keep in mind that an index can respond only to reported price movements in its con- stituent securities. An index will therefore reflect the stock market as a whole. or particular market seg- ments, only to the extent that the securities in the index are being traded, the prices of those trades are being promptly reported, and the market prices of those se- curities. as measured by the index, reflect price move- ments in the relevant markets. The index level will be affected by all of the factors that may at the time affect prices in the relevant markets for the constituent secu- rities of the index, including, among other things, appli- cable laws. regulations and trading rules, the market- making and order processing systems of those mar- kets, the liquidity and efficiency of those markets, and the prices and price behavior of futures contracts on that index or a related Index. Certain trading strategies involving purchases and sales of index options, index futures, options on index futures or portfolios of certain of the securities in an index can affect the value of the index, the prices of the index futures, and, therefore. the prices of index op- tions. These transactions and the resulting impact may occur at any time--and may accompany signifi• cant changes in the prices or volatilities of the stock and derivative markets—including at or shortly before an expiration. For example. traders holding positions in expiring index options or futures contr