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

But there are, of course, companies whose long-term fortunes differ substantially from the index. In this series, we look at how individual stocks have performed against the broad S&P 500.

Step on up, Duke Energy (NYSE: DUK).                                             

Duke Energy shares have slightly outperformed the S&P 500 over the last quarter-century:

Duksp

Source: S&P Capital IQ.

Since 1987, shares have returned an average of 10.5% a year, compared with 9.7% a year for the S&P (both include dividends). That difference adds up fast. One thousand dollars invested in the S&P in 1987 would be worth $19,200 today. In Duke Energy, it'd be worth $24,100.

Dividends accounted for a lot of those gains. Compounded since 1987, dividends have made up about 90% of Duke Energy's total returns. For the S&P, dividends account for 39% of total returns.

Now have a look at how Duke Energy earnings compare with S&P 500 earnings:

Dukearnings

Source: S&P Capital IQ.

Some underperformance here. Since 1995, Duke Energy earnings per share have remained roughly flat, compared with 6% a year growth for the broader index.

What's that meant for valuations? Duke Energy has traded for an average of 16 times earnings since 1987 -- a bit below the 24 times earnings of the broader S&P 500.

Through it all, shares have been fairly strong performers over the last quarter-century.  

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