Why would there be a difference of betas between S&P500 and Dow Jones as benchmarks of a portfolio?

We took five funds, all with 10 years of data and compared them to the S&P500 and Dow Jones (also with 10 years of data) to compute betas. There is a small difference between the two. I know that one reason is for the 500 companies in the S&P500 and the 30 in the Dow Jones. Can any one tell me additional reasons?

Tuesday, March 9th, 2010 Uncategorized

1 Comment to Why would there be a difference of betas between S&P500 and Dow Jones as benchmarks of a portfolio?

  1. Two differences:

    1. Dow companies are larger and more mature
    2. S&P 500 companies are smaller and more technological on average with higher growth rates

  2. Yorky on March 9th, 2010

Dow Jones Index

The Dow Jones Industrial Average (NYSE: DJI, also called the DJIA, Dow 30, INDP, or informally the Dow Jones or The Dow) is one of several stock market indices, created by nineteenth-century Wall Street Journal editor and Dow Jones & Company co-founder Charles Dow. It is an index that shows how certain stocks have traded. Dow compiled the index to gauge the performance of the industrial sector of the American stock market. It is the second-oldest U.S. market index, after the Dow Jones Transportation Average, which Dow also created. The average is computed from the stock prices of 30 of the largest and most widely held public companies in the United States. The "industrial" portion of the name is largely historical—many of the 30 modern components have little to do with traditional heavy industry. The average is price-weighted. To compensate for the effects of stock splits and other adjustments, it is currently a scaled average, not the actual average of the prices of its component stocks—the sum of the component prices is divided by a divisor, which changes whenever one of the component stocks has a stock split or stock dividend, to generate the value of the index. Since the divisor is currently less than one, the value of the index is higher than the sum of the component prices.
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