A day trader in her 20s will have much different view of stock diversification than a retiree looking to limit risk. Last week, we spoke about how to diversify a stock portfolio to both balance a longer-term view of your holdings while sharpening a shorter-term focus on factors that might necessitate changes. We're breaking this tutorial into seven sections: Understanding correlations Getting a portfolio started Is S & P 500 diversified? To better illustrate, let's consider the current make up of the S & P 500 — the diversification you'd achieve if you put an initial investment into an S & P 500 exchange-traded fund, or ETF. As of March 31, the end of the first quarter, the S & P 500 weighting was as follows: When you buy into an S & P 500 index fund, roughly 28 cents of every dollar goes into technology, while only 2.6 cents go into materials.

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