Thu 26 Apr 2007
It’s amazing to see the Dow above 13,000… an all-time high. But it’s interesting to realize what that means… what is really at an all-time high? The Dow is a price weighted index (read how splits and dividends are included if you really want to know), which means that not every component contributes the same amount to its ups and downs…
Different weighting is actually normal, but the Dow has an unusual weighting — it’s components are weighted based on price. That means that stocks with higher prices have a higher impact on the index (with some caveats — nothing is simple). In contrast, the S&P 500 is market-cap weighted, which can cause it’s own caveats and unusual behaviors…
A side effect of the price weighting is that (relatively) smaller companies like Boeing, 3M, and Caterpillar have a larger impact than larger companies like GE, Microsoft, and Pfizer. (more…)

