Investing isn't easy. Even Warren Buffett counsels that most investors should invest in a low-cost index like the S&P 500. That way, "you'll be buying into a wonderful industry, which in effect is all of American industry," he says.

But there are, of course, companies whose long-term fortunes differ substantially from the index. In this series, we look at how members of the S&P 500 have performed compared with the index itself.

Step on up, Dover (NYSE: DOV).

Dover's shares have easily outperformed the S&P 500 over the last three decades:

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Source: S&P Capital IQ.

Since 1980, shares returned an average of 13.5% a year, compared with 11.1% a year for the S&P (both include dividends). That difference adds up fast. A thousand dollars invested in the S&P in 1980 would be worth $29,400 today. In Dover, it would be worth $58,000.

Dividends accounted for a lot of those gains. Compounded since 1980, dividends have made up about half of Dover's total returns. For the S&P, dividends account for 41.5% of total returns.

Now have a look at how Dover earnings compared with S&P 500 earnings:

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Source: S&P Capital IQ.

That's pretty solid outperformance. Since 1995, Dover's earnings per share have grown by an average of 7.6% a year, compared with 6% a year for the broader index.

What has it all meant for valuations? Dover has traded for an average of 23 times earnings since 1980 -- not much higher than the 21 times for the broader S&P 500.

Through it all, Dover shares have clearly been outperformers over the last three decades.

Of course, the important question is whether that will continue. That's where you come in. Our CAPS community currently ranks Dover with a five-star rating (out of five). Do you disagree? Leave your thoughts in the comment section below, or add Dover to My Watchlist.