Adam Davidson has a great article in The New York Times on the flaws of the Dow Jones Industrial Average
More troubling is that [the Dow] ignores the overall size of companies and pays attention to only their share prices. This causes all sorts of oddities. ExxonMobil, for example, divides its value into nearly five billion lower-cost shares, while Caterpillar has around 650 million more expensive ones. Therefore ExxonMobil, one of the largest companies in history, pulls less weight on the Dow than a company less than a fifth its size.
The Dow, in other words, is weighted by nominal share price, not market value. And the oddities Davidson describes are not one-offs; have a look at the most recent Dow weightings:
Current Weighting in Dow Index
|Johnson & Johnson||3.84%|
|Procter & Gamble||3.74%|
|Bank of America||0.46%|
Some of these are astounding. Bank of America
How does this make sense? It really doesn't. The Dow may be the most popular, but other indexes such as the S&P 500 or the Wilshire 5000 give a much more accurate and reliable representation of the stock market -- and even they have their flaws.