LONDON -- The FTSE 100 is a market-weighted index. This means that not every constituent makes the same contribution to its performance. The value to the FTSE 100 of each share is determined by its own market capitalization. This means that the FTSE 100's largest company (Shell) has 190 times as much influence on the index as the smallest (Eurasian National Resources Company).

Here are my thoughts on the outlook for the shares of three FTSE 100 titans.

HSBC Holdings (HSBA -0.26%) (HSBC 0.29%)
HSBC Holdings, the U.K.'s biggest bank, has proven far more resilient and less volatile than its listed peers Barclays, Royal Bank of Scotland, and Lloyds Banking. This strength has long been rewarded with a premium rating to the rest. The result is a huge market cap and a large FTSE 100 weighting. HSBC accounts for 8.2% of the blue-chip index.

Despite this, HSBC shares are still cheap today. 2013 forecasts show an expected 11% increase in earnings per share and an 11.1% dividend hike. Despite this, the shares trade on a 2013 price-to-earnings (P/E) ratio of just 11.1 times forecasts. The shares are expected to yield 4.4% this year.

Royal Dutch Shell (RDSB)
Due to a quirk of how the company is incorporated, two classes of Royal Dutch Shell shares are in the FTSE 100. Adding the two together gives a total FTSE 100 weighting for the company of 9%. Shell has nine times the effect on the FTSE 100's value than the average blue-chip share. A large amount of the FTSE's future success depends on Shell.

Fortunately for tracker investors, Shell shares have plenty of potential to rise from here. The company currently trades on just 8.3 times EPS forecasts for 2013, with an expected dividend yield of 5%.

Vodafone (VOD -0.49%) (VOD -0.58%)
At the height of the dot-com bubble at the turn of the century, Vodafone made up more than 10% of the FTSE 100. Today it is "just" 5.3%. That still makes Vodafone nearly four times as important to the index as its sector peer, BT.

I hold Vodafone shares because I think that they are significantly undervalued. At today's price, they trade on a 2013 P/E of 11.3 and an expected dividend yield of 5.8%. The average FTSE 100 share is on a P/E of 16.4 and pays a dividend of 3.2%. Vodafone is a bargain behemoth.

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