Adam Davidson has a great article in The New York Times on the flaws of the Dow Jones Industrial Average (INDEX: ^DJI). The index of 30 blue chip stocks most of us pay attention to as the symbol of the broader stock market is, as Davidson explains, badly misunderstood, and its results easily abused.

For example:

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:

Dow Stock

Current Weighting in Dow Index

IBM 11.36%
Caterpillar 6.69%
Chevron 6.28%
McDonald's 5.93%
3M 5.17%
ExxonMobil 5.07%
United Technologies 4.72%
Boeing 4.42%
Coca-Cola 4.03%
Johnson & Johnson 3.84%
Procter & Gamble 3.74%
Wal-Mart 3.63%
Travelers 3.51%
American Express 3.06%
DuPont 3.03%
Home Depot 2.67%
Disney 2.41%
Merck 2.27%
Kraft 2.26%
Verizon 2.23%
JPMorgan Chase 2.23%
Microsoft 1.78%
AT&T 1.77%
Hewlett-Packard 1.70%
Intel 1.57%
Pfizer 1.24%
Cisco 1.19%
General Electric 1.13%
Alcoa 0.63%
Bank of America 0.46%

Source: IndexArb.com.

Some of these are astounding. Bank of America (NYSE: BAC) has a higher market capitalization than Caterpillar (NYSE: CAT), yet Caterpillar commands nearly 15 times as much weight in the Dow. General Electric's (NYSE: GE) market cap is just 9% less than IBM's (NYSE: IBM), yet it gets one-tenth the weighting.

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.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.