Shortly before 2 p.m. EDT, the Dow Jones (INDEX: ^DJI ) was down 0.19% for the day, while the Nasdaq (INDEX: ^IXIC ) was up 0.41%. While a 0.6 percentage point difference between the two indexes may not seem like a lot, it highlights the growing divergence between them so far in 2012. Even after losses this week, the Nasdaq is up 18.3% on the year, while the Dow Jones is up "only" 6.9%. Looking out even further, over the past five years the Nasdaq has gained 24.7%, while the Dow is up only 4%. Let's take a deeper look at what's driving the Nasdaq's outperformance.
The key reason
The biggest reason for the Nasdaq's recent outperformance centers on one key company: Apple (Nasdaq: AAPL ) . Just last April the company's weight in the Nasdaq 100 was cut from 20.5% to 12.3% in an effort to reduce the index's concentration in Apple. However, with Apple continuing to soar, it's now back to about a 17.5% weighting in the Nasdaq.
Apple's year-to-date return of 55.9% explains about 9 percentage points -- or nearly all of the Nasdaq's outperformance. As Foolish colleague Dan Dzombak notes, if the Dow had added Apple instead of Cisco back when it replaced GM in June 2009, the Dow would be approaching 15,000 right now, rather than battling to stay above 13,000.
Oh, and about that divergence between the Dow and Nasdaq today? Apple is up 1.18% so far today, so that alone explains a third of the Nasdaq's outperformance.
Another reason the Dow's lagging behind
Beyond Apple's absence from the Dow, there's another reason the index is trailing this year: The Dow's top performers hold little weight in the index. The top three performing Dow stocks this year -- Bank of America (NYSE: BAC ) , Microsoft, and JPMorgan -- comprise a combined 4.91% weighting of the index. The highest performer so far this year, Bank of America, is just 0.53% of the Dow. Compare that to the highest-weighted Dow component, IBM (NYSE: IBM ) , which is 11.93% of the index. In total, six different Dow stocks have higher weightings on their own than the 4.91% combined weighting of Bank of America, Microsoft, and JPMorgan.
The point? The Dow's big winners don't have much effect on the index. If every company in the Dow held an equal amount of weighting, the Dow would have returned 11.2% during the first quarter instead of the 8.1% it notched with its current price-weighted methodology.
So there you have it: The Dow's underweighting of certain outperforming companies and Apple's amazing run have conspired to hold the indexes returns down. In the end, that's why you're best off looking at multiple indexes beyond the Dow, like the S&P 500, to get a feel for how the market's doing at any given day.
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